Because it's illegal to mod.
Also, because PC has the potential for better specs. I'm mainly a console player myself, and I'm perfectly fine with both of those, really. In a lot of the cases, it's not actually frowned upon, just friendly banter. Some people take it a little too seriously though.
inb4 platform war.
I don't think it's illegal to mod single player games
But yes, PCs are better, but the game still runs fine in Xbox.