The short answer: we don’t know.
The long answer: it depends on what crossdressing is for you. If it’s a fetish (you’re hooked on the clothes, the thrill of doing something illicit, the purely sexual charge etc.) then like any other fetish, we don’t know. You probably have a good idea about what turns you on and why, though.
If you feel there’s something else to it, like acknowledging your feminine side, expressing your real self and so on, then perhaps it’s an innate part of your personality wanting some uptime.
Either way, we believe it’s healthier to recognise and accept all of who you are and what you like, and express yourself in whatever ways that don’t hurt or exploit others.