because you can do so much more with a PC and therefore the games are far more complex (and i'm not talking graphical engine but the variety of user interfaces (mouse, keyboard, joysticks...) along with having 20+ people all in a persistant world trying to interact with a common source at the same time... etc). Also you have many different software configurations.. some linux, some windows 95, 98, me, XP, directx 8.1, 9, other... ati cards, voodoo cards, geforce cards, some with old drivers, some with new ones. Some machines with only 64 megs of ram, others with a gig...
I'm sure the game worked perfectly on their 'standard' machines which represent a broad range of computers, but i'm sure you can get hung up with most of our 'custom configs' a lot.
Game consoles work all the time because the way you program them is so exactly specified and there's no variance from xbox to xbox, but I really don't think you'll find a game like SFC on a game console due to it's complexity but rather straightforward rpgs, 1st person shooters, and sports games.
btw I hated playing simcity on my super nintendo
enjoyed it much more on a computer.