Honestly it’s the monetization systems. I’m sure there are some fine mobile games out there, but they are drops in an ocean of low effort microtransaction factories.
The status quo right now seems to be gacha style games, which tend to be a thin veneer of probably anime fan-service girls over a deceptively addictive slot machine. The point isn’t to make a fun game, it’s to get whales addicted to the loot boxes so they pour fortunes into the game a few bucks at a time.
I doubt that most people actually care that a game is played on a phone, they’re just tired of watching the mobile game industry race to the bottom of the integrity barrel; and they’re afraid that the undeniably successful profiteering is going to continue leaking into every other medium.