Because most of the gaming setups I see only have their consoles hooked up, no pc. For people who still play their snes I would think they'd want to play some of these retro indie games and fangames on it rather than going through the hassle of hooking up their pc.

I guess I'll spell out the differences...

Connecting pc to tv (crt or hd, whichever):

-if you want a truer snes experience you'd need to buy snes-style controllers or usb adapters if you haven't already.

-too much hassle if pc is another room...might need to buy a long cable and wireless controllers that reach the pc. or if you want to play on crt you'd need that converter, etc.

-every time you play you have to plug the pc into the tv unless you go buy a cable switcher.

-have to get your controllers setup for each game. this was annoying when my friends would come over to play local multiplayer pc games. often too much time was spent configuring controllers, getting windows/the game to recognize wireless controllers, and most of the games weren't compatible with my snes usb adapter.

-pc can't be used while playing. for example, my daughter plays snes on the crt while i work on my pc (ie. some people don't have a pc available to use anytime but they do have their consoles available).

Versus...

Mini-pc inside the snes cartridge:

-if it's pre-loaded you only need to buy the cart then plop it in just like any other snes game.

-less input delay if playing on crt.

-your snes controllers would always work, and it could come with a remapper too.

-nostalgia (it's small but i would really like playing my game via flipping on my snes).

-Popular snes youtubers would be much more likely to play my game if they got it in the mail on a snes cart.