They allow themselves to become/remain desensitized to the more healthy forms of pleasure. Repeated overstimulation numbs the senses and either you need a break to recoup to regain pleasure or you keep agitating the senses which may cause pain. They keep agitating and pushing their senses to another level. They keep crossing and reestablishing boundaries of what they can or cannot do.

Their pleasure originates around control, violence, abuse, and/or conquering in taboo places. Eventually their experimentation crosses their treshold, and they get stuck (obsessive/complusive) in their hedonistic pursuits. (Not everyone gets stuck.)

I don't want to try to understand it any further. I like my boundaries! Maintaining healthy boundaries is my pursuit.