i dunno if its the reason but when pk came out my pc couldn't handle it yet so I never got into the game.. and by the time i upgraded my pc no one played pk
I hardly believe that is the reason. UT3 for example, also requires high end PC's and still I believe there will be a big community.
I believe the problem with PK was that the game sucked arse at the beginning. It needed a lot of mods before it became playable. And we saw the same thing happening to Quake 4 ... unfortunately.
GL Painkiller Game! At least 17 Buyers ;)