-They don't want to pay child support.
-They feel that if they're known as a man that supports "Pro-Choice", that reputation will get them laid (more) by a current, or prospective (future), female partner(s).
I would reduce it to basically your first and last suggestions. More broadly:
- they don't want to take responsibility for a child and get thrown into #adulting (I was guilty of that for years)
- they know it's the only socially acceptable position to hold, and they want to be popular