Technology

This. Components would be overpriced and proprietary. Nobody wants that.

Building and upgrading a computer really isn't that difficult. All the parts only fit in one spot. Getting compatible parts can be tricky if you don't know what you're looking for...but this problem could strike this idea, too, because there would certainly need to be different generation mainboards whenever CPU sockets or chipsets or memory speed or really anything else on the mainboard comes around.

So such a solution would likely lead to less choice and more proprietary vendor-locked garbage. Just now solely on the hardware side.

But wait...what games are compatible with this system? What games will run well?

This is something Valve has done really well...they built a benchmark system. This is the problem that's been plagueing PC, imo. AAA games get built for bleeding edge tech, necessitating upgrades...while the steamdeck sets a bar that developers have to be playable on in order to tap that entire market. Could the game run better on better systems? Sure, probably. But it needs to be at least playable on steamdeck.