My 2 cents:
I’m seeing (actually hearing) speakers more and more. Most of the time it’s at cycling venues that are more extreme (lift parks, jump parks, etc.) and sometimes they trickle onto trails other than that. I guess the busier the trail the more there are issues with riders; at our local trail systems we can have 50-100+ riders at a time of all sorts of demographics during popular times. Many aren’t aware of mountain bike “rules” or “common courtesy” and trails get rutted in rain, people blare music, ride the wrong way, etc. If you’re choosing to ride at a popular time on a popular system you take inherently more risks of everything, including behaviors you don’t agree with. It’s the same with hikes on popular trails on weekends, road bikes, pick-up basketball, even driving motor vehicles, etc. It is what it is.
Now if I’m miles deep in a remote forest then I think the speaker is annoying AF. But hopefully it only happens very seldom.
As for my thoughts on music? Busy trail, no music. Not busy trail, i’m ok with ear buds but if I start seeing multiple people I usually take them out. Speakers? If there on low volume, that’s cool by me, my cassette hub is pretty loud too!