Or is fed up with loud music while trying to enjoy sunset at the beach.
Exactly this. It also depends on social skills of the one requesting turning down. Maybe most of the times I skipped even trying to ask because I thought situation was hopeless, someone would actually turn volume down, but in my life I think I didn't even have 30 situations like this. I live in a place where it's rather quiet and poeple just don't push out loud music for long periods. If they do, it's rather sporadic and they try to respect social norms. I also know that I should not be an ass and let other people have fun, that helps too.
This is just the kid on the bus/train playing music on his phone speaker. Wear headphones or play the music at a noise/distance that doesn't disturb others.
But alas, we live in the real world. Sometimes people act in ways we don't like, and we can (and should) talk to them in that case, worst thing that can happen is that they say "No thank you" and then we either deal with that or leave.