probably lots of reasons, but I can certainly see someone who's used to having anything they want at any time also wanting to be put to sleep (pardon the term) whenever they want as well. if all of your life is 'on demand', why wouldn't sleep be as well?

You can get addicted to propofol, and some people who self harm frequently and severely report the propofol as one factor for their continued self harm. (although it's often only one of many factors).

I understand he suffered from chronic pain, so sleep must not have been easy for him. I can totally see the lure of propofol in such a case.

I guess he was a troubled character? Couldn't sleep normally, perhaps due to some trauma?

Arguably the most talented and most troubled child prodigy/musical genius of all time. Obvious trauma right off the top would be a childhood of physical/sexual abuse combined with an unprecedented level of early fame and success.

Reportedly, he had some botched plastic surgeries which made it hard to breathe normally, and in particular, made sleep painful.