Then you get old
I was reading the post "When Did So Much Become So Little" by Brendan Kelly (lead singer of a few bands I used to listen to in high school, namely Slapstick and the Broadways) and came across this in the comments and it really hit the nail on the head as to why I don't play music or write songs anymore.
"Then you get old (band old, that is). I'm 28 now, and most of my close friends from my musical past barely play in any band capacity, no matter how much they'd like to, or how talented they are, because they'd rather give it no attention at all than try to fit a reduced version of it into the semi-responsible adult life they're trying to live (kids, house, taking care of parents, or whatever they're working on). It's just depressing for them, I think."