There are multiple reasons, first of all, almost everyone who was waiting for GTA V on PC has already bought a console and has already bought GTA V. Why should they buy it again on PC? Second of all, it's clear how GTA V wants people to play their game, no hacking, no cheats at all, this is easily possible in GTA V if it gets released on PC. I'll bet you that after a few hours of GTA V's (if it gets) release, people will have already made hacks for it, made cheats for it, made mods for it, and so on. So this is more like, "Why GTA V WON'T be released for the PC", because R* wants their games to be taken seriously, but that being said, even on PS3 people have found bugs and exploited them.
Kid, to be honest ur a console worm.
U didn't even know and saw what mods does with GTA IV and how they extended the game life, or even how cool is to run a real model of ferrari 458 italia in the game u like, and not a fkin fake that R* do. So many racing games have real cars for theyr models and R* is still using to made jokes in theyr game...
Hope my post will open ur eyes a bit.
I think Rockstar doesn't use real cars, because most companies don't want their names associated with a game like this. Racing games are one thing, but a game where you torture and kill people is quite another.