Had they chosen not to release, in increments, the entire game, they would have had my money on day 1. Rather they chose instead to divide and trickle what was one game into a "trilogy". I won't justify piracy, my choice is to simply wait for the price to reflect the product (yes yes, hate me for not worshiping the game as much as you if you must), but the drive to do so is not alien or inexplicable, and no, I'm not suggesting this is the exclusive reason behind piracy. Of the people I've seen talking about it that have chosen to pirate this game, it is certainly one of the most prevalent excuses made.
"But if they didn't break it up we wouldn't have seen this game for another decade"
If you genuinely believe that, there's nothing I can say to permeate your logic.