And non of the games on Steam are Nintendo games. Sure you’d could use an emulator but the average mainstream casual gamer can’t be bothered to learn how to do that. And Nintendo is a much better known brand than Steam with the casual crowd. Nintendo is not really competing with Steam. Smart phones, which most people already have and the games are free, are a much bigger threat to Nintendo than the Steam Deck.
At this point, anyone with the tech knowledge to have purchased a steam deck can install and run emudeck in like 15 minutes. You just go over to desktop, download and install the single package, put roms in the correct folders, then run the program and everything is already sorted into collections with you can find in the game mode library.