For me, part of it is a simple fondness for understanding things and a separate but closely related joy in making things that "go", things that act "on their own" as it were. I always kind of assumed it was an innate propensity, a kind of natural monkey curiosity. I was always taking things apart as a little kid. They say I disassembled the clothes dryer one time, but I don't remember it.

I like it when something goes from being mysterious magic to a familiar tool. (Like compilers.) And it's even more fun when you can use your tools and knowledge to create some new useful or beautiful (or both) thing with them.