> This isn’t iOS or a game console

And iOS and game consoles aren't even the only handheld gaming devices. There are lots of options (Android phones and tablets from dozens of vendors, Steam Deck and its many competitors, Switch 1/2, PS Portal, etc.)

But presumably developers see value in being on the leading game stores (Steam, Google Play) for hardware from multiple vendors, and on walled-garden game stores (iOS, Nintendo eShop, etc.) for single-vendor hardware.

They don't have to publish on Steam and Gabe doesn't need to take that much of their money if they do. There's no reality where that money is better-spent paying for new carpet on his fifth yacht instead of supporting the indie creators.