I really don't think Fortnite is as bad as you're making it out to be (certainly not even in the same league as most mobile microtransaction fests). The core of Fortnite is a pretty good (imo, although I prefer Apex Legends) battle royale fps, and the microtransactions are purely cosmetic items.

In contrast a lot of the big mobile games are barely even games. They're just AI controlling your gambled for gacha characters, which are very not cosmetic only. And the games that aren't AI controlled are still just basic turn based battle mechanics with very little strategy (and what is there is vastly less important than just getting better characters, probably by gambling).

I suspect the market of "people who play mobile games" and the market of "people who play PC games" are not even the same kinds of people, and if you tried to release the same stuff that makes money on mobile on PC, you wouldn't actually attract many new players. Likewise if the mobile market ceased to exist overnight, I doubt the players would be that attracted to many PC/console games. They're getting different things out of them.

Of course this is all just speculation, I don't really know.