In my opinion, earbuds on the trail is a no-no, mostly for safety reasons. You’re completely oblivious to anything outside your field of vision, including oncoming cyclists. Just had one rider collide head on with another on my favorite piece of trail, and they weren’t even wearing earbuds. Broken ribs, punctured lung, and a nice stay in the hospital. The hazard is real.
Furthermore, a cyclist with earbuds creates a terribly frustrating and hazardous obstacle to pass.
Being on a bike in public requires operator awareness and vigilance. I’m open to another view on this, but I currently just don’t see how earbuds can be considered acceptable while operating one.
Hikers/runners should also maintain awareness when on shared use trails. Sat behind a “stroller” just the other day for 30 seconds, wearing earbuds, had no idea I was behind him waiting.