For everyone it's different, for myself it started off as "I wonder what that would feel like". Obviously any mentally balanced person would never have that kind of thought occur, but it was curiosity that started it. Then I became more interested in the sensation and it almost started to become addictive.
So yes, I think the want to feel anything at all plays a big part for most people, and a lot do tend to find it addictive too.
I've noticed this happens often when you already own something in the bundle