Do you think there are illegal instructions in the music or coming over the headphones?
Do you think a player will not pay appropriate attention due to the headphones?
Exactly what is the use/value of making headphones illegal?
I'm betting that part of the reason for not allowing headphones is the possibiity of folks having cellphones connected to them, and getting "assistance" in the form of coaching and such. While it should be a reasonably easy determination, many folks play their music on their phones, and probably a lot of TD's aren't interested in becoming so tech savvy that they can figure out which are simply players vs which are phones. Thus it's simpler to not allow them at all, and not have to worry about figuring it out on a case by case basis.
Just a guess. I've never heard a reason described.
So far as communications issues, I think that's BS, as well. As I suggested earlier, if the wearer is actually paying attention to the match, if any communication is necessary, the wearer will see his opponent speaking to him and can simply take out one of his earbuds. Heck, the wearer might just take one out when not shooting as a regular course. That's what I think I'd do.
I have resisted wearing headphones because I don't want to become dependant on them, and APA doesn't allow them at their events. (On our regular league nights it isn't enforced, but any state tourney will prohibit them, or heaven help me, Vegas.) I have been tempted several times, from a concentration standpoint.
It doesn't matter to me what kind of music is being played on the jukebox, I've heard and/or played (between DJing and drumming) pretty much everything before, so music stopped phasing me years ago. I like the idea of drowning out the chatter around the table. THAT distracts me. I know, I need to train myself better. A work in progress...