I have noticed the same thing. Having muscle makes men instantly respect you because you have something which they don't have, but probably want to have. It also shows that you are disciplined.
I think it's also partially due to a bias where people assume that you are a more respectable or "cool" guy because you have muscle. At least that's what I've noticed. As soon as I got muscle I became known as a "cool" guy at my school despite really being more of a nerd. People also for some reason think that I am really confident because I don't speak much and I'm always relaxed, but its really just shyness.
So yeah, having muscle just makes everyone assume that everything you do is cool even if you're doing nothing remarkable.