Size. Not everyone has ginormous hands. The steam deck feels big and unwieldy despite being fairly light. I also don't like the ergonomics of the steam deck, and I would miss the colours and so on. But also not everyone wants to emulate Nintendo games. Half the fun of animal crossing was sharing experiences with other players online. Same with smash bros. Emulation isn't at a point where I would consider it to be for the masses and certainly not for a lot of kids these days.

The steam deck is a great device and there should be competition in this space of portables. But not everything about it is perfect for everyone.