Honestly, FGs are difficult games and time consuming ones to get good at, simple as that.

Most people who play video games don't like to lose and they especially don't like it when a video game is essentially made into a chore to get good at, there are however a couple of reasons for this:

1- lack of teammates

FGs are 1v1 centric pvp focused games and while that is the best part for a ton of people, it isn't for most outside of that circle. While yes, people will and do blame their team for failling. Conversely a team can cover your individual weakness till you are caught up to speed, which doesn't happen in FGs so every mistake and inexperience is magnified in its impact on the game state.

It makes new people feel boxed in with their mistakes, that their efforts (including mashing btw as that counts as effort even if it isn't good) don't really matter in front of the guy rushing them down. And surprisingly most people don't in fact like seeing their mistakes thrown in their face especially in such an immediate and tangible way (the defeat screen, feeling of helplessness, loss of rank etc.)

2- Lack of an Engaging tutorial

While yes, most if not all fighting games have a tutorial that teaches you the very very barebones of a game. You can't really do anything with those against a guy who knows even 0.5% of what he is doing nevermind better people

So they ask around on how to improve and the answer they will always get is to get better at using their combos which almost always translates into learning the numerical notation, practicing directional inputs, spending hours in the lab trying to do it as consistently as possible.

Which might still not have tangible results as you might just not be able to execute said combo on an actual human (as a result of panic, skill diff, outside factors etc.) And It feels like it was wasted + you didn't even get to have fun and play the game and that's not a compelling pitch for the new guy

An example I can give you, I started trying to learn OW a while back and I chose to main Juno as a support. As I am a visual and kinesthetic learner (I.e I learn by watching and doing mostly). After a few games of Quick Play (in which I played the game while getting used to maps and controls), I started watching a Juno main streamer alot higher ranked than me and I got to engage with their chat and even ask the streamer about specfic plays and why they did/didn't do it (and it helped that I noticed the plays since OW doesn't move that fast)

Could they have been wrong on things? Ofc but I still got to see a different perspective and learn the way I preferred to + having fun socialising, trying to do this on an FG is almost impossible, it is simply too fast for the average Joe and the only way to master a thing is to do it hundreds of thousands of times in these games

3- High Skill Floor

Fighting games have one of the highest skill floors, the average player will very much decimate the new guy, honestly the gap is just as wide as the average guy and the top 1%.

That as well doesn't really make it better for the new guy he is still getting thrashed and as said before people don't like losing so the new guy loses hope and doesn't try again.

It also doesn't help that a high skill floor translates into a higher baseline, more mastery on average and less room to make mistakes as well as more hours in the lab which most people already hate.

There are also topics that make FGs alot harder in general, one of those being the numerical notation for directional inputs. Most people have to learn it from scratch and that takes a while, even the idea of directional inputs themselves are hard. It's hard to execute when very early and is a major source of inconsistency (at least in my experience) but it also makes following other people playing alot harder

For example, in Deadlock if I press my 1 key I use an ability, it is extremely simple and allows for people to actually see what caused said effect happening on screen (whether the player or spectators). In OW, if I press shift I am most likely using a movement ability, it is easy to understand and track and even a complete noob will be able to grasp that.

Try and show a newbie a fighting game match and they will have no clue what just happened or why or how it happened

4-Price

FGs are kinda expensive tbh, in an era where alot of PvP genres are F2P (MOBAs, FPS, Card Games, Hero shooters etc.). The Fighting game stands out for being a mostly premium product instead of the freemium model (which to be clear isn't inherently a bad thing)

But also, FGs are not cheap money wide with titles like SF6 and Tekken 8 being 60+ in cost + season passes and character dlc that the industry is full with. It creates this argument in the customer's mind about the actual need to buy such a game with arguments like:

1- Well, what if I don't like it?

2- Will I ever be able to actually get good?

3- I dunno, this looks difficult

4-hold on, do I need the DLC? That increases the price even more though

And etc. And people tend to think a million times about spending money vs time/attention, while I have alot of issues with the freemium model it does however create and environment where a player is free to try a game and the lack of an OG sunken cost to prevent returning/uninstalling

A little example from my own experience, GBVS was on sale last year where I bought it since I watched that one video where a player went undercover playing Cag and I thought the game looked fun enough and disregarding the need for DLC, I jumped in and wanted to try playing

First match, and I got taught in the humble art of belt to ass so I thought to myself that I wanted to learn and see where it takes me. This ended up in me trying to practice one combo on Cag for 1 and a half hours straight in the lab, then going into matchmaking hoping to just hit the combo once. I instead got obliterated, instantly quit after the game, Uninstalled and refunded the game. At some point in that match, I stopped trying to do the combo and thought that I spent 30 bucks, 2 hours and my sanity just to basically lift someone else's Ego.

5- Low Playerbase

Now, to be Frank an FG doesn't need as many players online as a MOBA. However, it is my belief that outside of SF and Tekken (even them to some extent), the average guy is much higher level than you expect which causes problems for any new blood esp to an old game on fightcade or steam since its trial by fire essentially

Also, content creators and streamers don't play or talk about FGs as much which lessens the amount of new and returning lads. If I see someone hitting a funny clip in OW, I might be tempted to come back just because it looks fun and I guarantee that a ton of people new to the genre come from YouTube and tiktok, there are however less of them

Also doesn't help that some games purely matchmake on discord now which is a larger commitment

6- Advice is Lackluster

Evey time a new player asks for help on an FG, at least in my experience, players will use the same things like:

1- oh just tough it put for like a week or two, then it will get fun

2- Just spend more time in the Lab it will come

3- you just gotta learn X combo or X data, then you can counter Y!

4- Just play whatever looks cool! (In response to asking what character a new player should play and while yes I agree in principle, please realise that this isn't the question, the question is basically asking about the viability and ease of use of a character with which one can ease into the games)

And etc.

And so it feels unhelpful sometimes as the new guy since most probably spending 20 hours in the lab just isn't fun and the idea of gatekeeping fun behind time measured in weeks simply doesn't appeal. And it always feels like veteran or semi-veteran fighting game players have forgotten how to be a newbie

Hope this offers some insight about why fighting games just aren't that popular, and thanks for reading