My point is that even pre-built PCs are cheaper and better in every way other than size.

Size is a big factor here. Steam made a console sized PC.

There isn’t a lot of PC case that size. And the list of PC parts for SFF are limited and more expensive than their normal counterparts.

So yeah, if you want a full tower PC in your living room, don’t buy the Steam Machine. But I haven’t seen a PC build of that size cost less.