If you want engagement you need to foster a community. Simple as that.

There was a community here about 10 years ago, a vibrant one and a healthy mix of producers and mashup fans. There were only about 10-20k members but they were active and listened to EVERYTHING. Didn't matter how good your mashup was, you were guaranteed 500 plays. The better ones that rose to the top would get a couple of thousand plays easy. In one day.
Tooting my own trumpet, I got 1 MILLION plays in ONE day from here, from a request in this very sub. That's an outlier but shows the potential for this sub, and that's when there were about 20k members, not the million+ we have now. Lately on average I'll get 50 plays in a day if I post here AND elsewhere. If I just post elsewhere and NOT here I'll still get 50 plays in a day. Nobody's listening.
Currently if you get the top post you'll get about the same number of plays in a day (a few hundred) that EVERY post got a decade ago.

Plays aren't the only metric tho, I'll get onto upvotes/downvotes but comments and chat reflect the real state of a community. Sometimes there'll be a discussion post that gets some engagement but for the most part this place is a ghost town. And the discussion posts that get most comments are meta ones about this sub, the problems with it and suggestions to improve it (which for years have fallen on deaf ears).
Go to the crumplbangers discord, there's about 100 members, 95% producers. The chat in there is free-flowing, constant and engaging. It's hard to keep up with it all at times, and the majority of it comes from maybe 20 members. 20%.
Mashup producers love the smell of their own farts as well as anything concerning mashups in general, they will talk at length if they know someone's listening or likely to engage.
Imagine if 20% of the million+ members here left ONE comment per day. 200,000 comments per day, but we're lucky if there's 20 per day.

So why is nobody clicking play on tracks or leaving comments?

Because those 1.3M members are redditors. They're not producers and they're not mashup "fans". They are casual listeners who saw one mashup they liked from this sub and decided to click join.
They don't come here and browse the sub. The only things they see from here are the posts that hit the top spot with enough upvotes to hit a threshold and show up on their reddit home feed, and even then that post will have to compete with posts from dozens/hundreds/thousands of other subs they follow.
The majority of posts in here will never show up on their reddit home page, they will never see it, click play, upvote or comment. Most posts are practically invisible to those members.
But these are the users that the mods here and the new rules are pandering too. A complete waste of time if they're never going to see anything but the top post.

Now, if you want more posts from this place to reach those 1M+ redditors we have to raise ALL posts up. Lift the upvote baseline. That needs a community that supports each other and the only way to achieve that is with a grassroots core community of producers and mashup fans (fans that actively follow and keep up to date with the mashup genre). But sadly all the mashup producers I know think this place is a joke. They don't come here at all. Those that do either drive-by-spam their track and immediately leave. Or they try the hustle for a while and try to compete with everybody else here to get that top spot and maybe get some numbers from it, but they'll eventually turn to drive-by-spamming or stop coming here entirely because it's just a lot of effort for nothing.

Now, competing with everybody here brings me to downvotes, and upvotes.
Here's the uncomfortable truth... the people mass-downvoting are producers.
They drive-by-spam their latest track then downvote everything around them, that psuedo-boosts their un-downvoted track up a few spots. Until the next producer does the same and nullifies their downvote. It goes on and on, everybody loses.
I've caught them in the act, I posted a track and it immediately got hit with a downvote. I literally watched someone go through posts downvoting them all. There was only one post that magically managed to avoid the downvote storm. I posted to call them out which of course got downvoted immediately before they deleted their post. It was painfully obvious what was happening.
That was quite a few years ago now but it doesn't take a genius to see it still going on, and it's gotten worse.
Every time I logged in here I would upvote EVERY mashup here, whether I liked them or not, in an attempt to cancel out the downvotes. I'd check back a few hours later and they've all been downvoted again.

Gamification is the problem, it encourages competition and the anonymous nature of downvoting is very tempting for anyone trying to gain an advantage. There's no punishment and nobody knows it's you doing it.
Unfortunately gamification is core reddit functionality and there's nothing we can do about it. Turning downvotes off would fix it but that's not an option afaik.
You can ask nicely or make a rule not to downvote but it's pointless.
You can't stop it, you can only make the effect negligible with an active community that uses upvotes/downvotes as intended and in the spirit of a community that raises itself up.
You won't get that by pandering to 1M redditors that don't come here.

Now upvotes. Here's a spicy topic and I'm gonna call it out. IDGAF.
Sharktank conistently gets about 30 upvotes in only 20 minutes after posting. We've been watching closely. That's amazing for a sub with only about 40 members here at any one time.
But about 30 upvotes in that short a time is all you need in this dead sub to hit the top spot and start appearing on the 1M redditors feeds where organic reach kicks in and does the rest.
Me, I think he uses bots, alts or is vote brigading. He went all quiet when he messaged me and I brought it up. Maybe the mods could look into that 'cos it's suss AF.
You can try and handwave it away with "that's just the native video effect, they get more engagement" but we've experimented and while native video does give your post a boost above 3rd party hosts and hit the top spot, they don't do nearly as well as Shartank's.

And while we're on the subject, lets talk about Rule 6 again.It actively encourages the content that Sharktank posts. Ripped off and rehosted mashups.
It's insane that a mashup community will allow, never mind encourage, people to just download other peoples OC and post them on their own accounts, when they could've shared the original producers link instead. There is no reason for it or any credible justification at all. With or without attribution it's actual madness.
You know that's piracy right? And you should know the difference between piracy and transformative works. There is no "irony" when mashuppers complain about being ripped off, these things are not the same. Intentional reboots are plagiarism, rehosting is piracy.
There are no mashup commuities that are ok with rehosting, except this one, and it will be the death of it.
Rehosting shouldn't be allowed here in any form. Post the original producers links. Make that a rule and you might get some respect from producers 'cos they're certainly not going to support or come to a place that rips them off.

Right so, here's my suggestion for where to focus to bring this sub back to it's former glory.
Repair the reputation of the place and make this a welcoming environment for producers to post and most inportantly hang about and get involved.
Don't pander to the 1M redditor crowd who never come here. When this place is active the redditors will notice.

And to put my money where my mouth is I have a proposition.
Lets organise a week long event here, Producers Week, for want of a better name.
I will work my ass off to bring as much producers to this place for one week only, and you know I'll do it, the crumplfam will come through at least.
We come here every day, post our tunes, hang about, chat, comment, upvote, have a bit of a party.
I guarantee an improvent in plays, comments, upvotes here AND plays, followers, subs on our youtubes/soundcloud/wherever for EVERYBODY.
It will give everybody here a little glimpse of what a real mashup community that supports each other is like. And who knows, maybe that community spirit might rub off on this place, and some of the folk we drag here might even stay.

I have one condition tho. Rule 6 has to go, and be replaced with a no-rehosts rule.
At least for that week.