I'd say it's like this for any older game which still has a multiplayer community regardless of genre. There just isn't a big influx of new players and the bad ones give up.
In MtG or LoL, a worse player than the opponent might still win 40% of games (luck of the draw or teammates), even ignoring matchmaking systems.
Players can aim for losing less over time, while still having a chance to win any particular game.
In SC or chess any chance of success against a better player is effectively zero.
This kind of thing hasn't really been tested in RTS games, which usually focus on 1v1s.
I think "playing like a human" can still be an issue depending on the game. Until people want to play against AIs, there's not a lot of work put into making AIs human-like rather than just AI players.
Also there still Starcraft 1 AI tournaments which are interesting. https://youtu.be/gqggsFpTAt8
I didn't know they were still doing SC1 AIs, I always wanted to make one but never quite figured out how to get started.