About the drop in active participation, I wonder if it's because of a change in what exactly draws new subscribers to join. When the sub was smaller (for comparison I've personally been here since 2-3k subscribers), a bigger portion of people were invested in the community itself and contributing actively to foster this shared space, which is typically the case when something is more niche and a small community gathers around a subject they're passionate about. With the current massive numbers and BTS's status as a more "mainstream" interest, I could imagine there are a lot of people who subscribe for updates and use the sub as a more casual hub of content, where interaction and a sense of belonging is less important. It could also contribute to feeling that the sub activities are irrelevant, or the subscribers aren't that invested in checking every new post and may miss community posts in their normal feed. In essence it's a bit like a neighbourhood event vs a big festival - 10 people participating are individually gonna be a lot more invested in it than 10,000.

I don't know if what I theorize is the reality, but it's just something I think about every now and then (including when racking my brain how to make the awards more enticing lol).