1) Money. And I started because it's indoor work with no heavy lifting.
2) Zombies, mostly. Don't believe me? Check out the questions in QA. Zombies would appear to be writing most of them... :sigh:
In all seriousness, this isn't a "quick answers" type question - it's a discussion starter - which is probably more the kind data you need anyway.
I'd suggest taking this to the forums:
The Lounge - CodeProject[
^] might be good, but do expect some abuse and a lot of contradictory suggestions.