Could be in part they were trained to be that way by their abusers. look at those of us here that self unjure because we have memory pieces that contain self injury behaviour of when we were made to hurt ourselfs or others, there are also many here that through abuse were forced to sexually abuse others. why not BDSM acts too? Some people who have been abused may gravitate, crave, need and or get aroused by that kind of thing because they have been trained to do so.