I pirate games for several reasons. The main one being the number of times I've bought games that were bad, buggy, and/or incompatible with my hardware, coupled with the inability to return it once the package has been opened. For example, I bought a move controller and Tiger Woods PGA Tour 11 for the PS3, only to find that it doesn't work left-handed. In total, I wasted almost $150. I spent $50ish on Elder Scrolls 4: Oblivion only to find my save games hopelessly corrupted, with no clues as to how to prevent older saves from corrupting again.
In most cases, I'll download a game in order to find out a) Whether it's buggy or incompatible, b) a good game or not, and c) how much DRM it's utilizing. Anything using secuROM is an automatic "Will never purchase". If it works without crashing every 5 minutes, isn't a decent, enjoyable game, and employs only modest DRM, I will go out and purchase it.