Honestly the reality is mobile games just developed a horrendous development culture and incentive base.
What I find kind of baffling is why did mobile gaming manage to effectively kill pocket sized gaming systems. IE I'm seeing the positive sign of the semi-portable systems. IE Switch and steamdeck...
But the gameboys and PSPs were basically killed by mobile phones. But they offered, basically quality games... yes 4+ generations behind existing PCs and consoles. But fun complete games that were worth $20-$50 to drop, and actually get many hours of fun out of.
There really were some great ones. Playing through Metal Gear Solid: Portable Ops still stands out to me over a decade on. Shit was tight, and I honestly didn't feel that again after the PSP. Until I picked up my steam deck, that thing would have rendered 10 year old me catatonic.
and that's a thing to me, IMO I don't think that there wasn't potential to make good mobile phone games... or say for developers of phone games to default to allowing a standard clip controller etc...
But even with the basic limitations of a phone as a controller, it's worth noting that the real fall of mobile gaming was just the rise of the shitty, microtransaction to progress games. That can be seen with the trajectory of even games that were origionally well loved mobile games, hopping on that bandwaggon (IE angry birds, plants vs zombies etc...)
A. For controls, power, and screen resolution, mobile is just the worst. If a game on mobile tries to imitate a controller, it takes up a while lot of screen space. If touch is used more like a mouse, I've never seen a game that needs touch specifically.
B. Mobile is a better platform for the shitty pocket casino games. When it's impossible to leave the device at home, it's much easier for a game to develop an addiction. That's why mobile games like clash of clans get users paying upwards if $100,000.
It also sucks that when you buy a game to own it often isnt maintained, so upgrading your phone or sometimed even just OS updates will break the game with no fix, no recourse. I got real fucking tired of losing my purchases to that shit.
Notably I played the ever living shit out of xcom enemy unknown and would have kept doing it too if it weren't for this issue.