Piracy to me is what used to be called Demo. I actually have bought games because I fell in love with them, after playing the pirate version. I have even bought shows, biggest buy for me being StarGate 1.. but that was when money problems have not consumed me.
Another reason is all the shitty DRM some games have pulled. I do not accuse the companies for trying to protect their product.. but putting first their own selves and then their consumers, definitely is something I hate. I have bought Spore back in time and never even touched it. It is one of my favorite passtimes ever, but the DRM was simply stupid. I do not remember why I could not install it one of the times I wanted to play it, but I remember I had to communicate with EA and ask them to unlock the abily or some shit like that... yeah.. no.
Strange as it will sound, I hate Steam (which is the only way to get so many games), so even if i buy games on it, I still keep them pirated on my PC. I do not per se know why I do not have to have steam around in my PC and the only times I use steam along with games, is to just play on steam for some minutes, so I can write reviews on steam. One of the main reasons, is because with Steam I feel restricted. I want my games other times in C:\Games and other times in D:\Games, not C:\Games\Steam\even more steam\steamengine\wherever\. Not to mention that it can potentially give problems with games that use mods, like seeings mods as the game being damaged and wanting to restore it or whatever.