Honestly, it's just fun to blow leaves or snow. It's a mindless puttering activity that lets you improve your home area and be mildly active.
Unfortunately what happens is people's general tendency to think about themselves and nobody else. So they're self-satisfied in their reasons for being out there, not thinking about the dude next door that works nights and can't sleep, and even his construction-grade noise headphones don't help. Or the dude that just wants to listen to jazz quietly.
The leaf blower people are well-meaning people with mild mental illness who are just selfish enough not to realize their home/self care is annoying others. e: A lot of times the guy just needs to get the F away from their spouse. I've lived near leaf blower people and they're invariably older married (sometimes retired) men. Never women.