It is addictive behavior which often revolves around sexual arousal or gratification. Sometimes, simply attention. For some, the arousal is about feet, for some it's amputation, and there are those who are aroused by dead people. Andrew Luster (cosmetic heir) had a thing for comatose individuals, women he could "have his way with" who mentally were not there. I think it is a combination of a predisposition to addictive behavior and that individual's life experiences. I would assume the best way to treat an addiction is with addiction therapy and drug therapy but the success rate for addiction therapy is not particularly high.
The article, "A New Way to Be Mad" describes a "fad" if you will, during the 19th century (I believe it was then) where amnesia became popular. The "fad' eventually disappeared. Multiple personalities became popular for a while then that began to wane. I think that transgenderism will do the same. For many, it's a fad. Lesbianism was a fad during the roaring 20's. The fad is beginning to return for various reasons, some of it about attention, some of it about rebellion, and some of it about the "cool" factor. From what I've read, for some, the urge disappears because it no longer satisfies or something else takes its place or reality sets in on how the fetish may be destroying that individual's family or imposing unfair hardship on others. Some take the fetish further (such as with the amputation fetish where the individual may graduate from admirer to amputating a toe now, a leg later). This is a very rare fetish.
Much of this is perpetuated through the internet (lots of encouragement from anonymous cheerleaders) and provided an acceptance factor by the media and validated by laws passed such as what Gray Davis has done here.