My guess are people who want to PC game but don't want to deal with building a PC themselves - there's a decent market of pre-built gaming PCs that this would be competitive with.
https://www.newegg.com/Gaming-Desktop-PC/SubCategory/ID-3742
Custom gaming PCs are huge and ugly, which is a concern for me (and my partner). Size and comfort are the main advantages.
And there's a valid market there, but as someone who just spent half my Saturday morning debugging a CPU throttling issue on my kid's 2020-vintage Lenovo Legion laptop, I feel like a pre-built is in some ways the worst of both worlds, like you don't get the savings and fine-tuning that is something you assembled yourself, but you still get all the fun of debugging driver issues, weird performance stalls, and who knows what else.
That said, I've never had a Steam Deck or tried to seriously game on Linux, so I may be out of touch with how much smoother the picture is in an all-Proton world.
(the laptop issue turned out to be something in the firmware asserting BC PROCHOT for some reason; for now we can periodically clear it with the ThrottleStop utility, but who knows what the actual underlying problem is)