I think I know why the games dying. Matchmaking and team play.
I was watching Dyrus the other day and he went on a rant about how the games just not enjoyable anymore (Every streamer does these days). Normally I'd just pass this off as normal complaints, but in that rant he had a really good point - That every popular game right now all has one thing in common and that was the ability to win by yourself.
Today I decided to play some League with my friend, and of course the first game we had someone with 18 deaths... while everyone else on our team averaged 4. In other video games, this wouldn't be a problem, but in League, a single player can spiral a game so out of control that every player might as well be spawning under an AC-130 killstreak. The game can be unwinnable from actions that are completely out of your control and that's anti-fun as a core mechanic. My friend had no desire to continue playing for the day after that negative experience.
Well, good thing League has balanced matchmaking?... Nah, we're going to force 50% win rates and intentionally throw in players that normally wouldn't be in your games... to balance out a player that also shouldn't be in your games rather than matching everyone equally. Players are getting burnt out from this and moving on.
Team play used to work in longer games that required thinking, but as games become shorter its becoming the nail in the coffin.