Here is a plausible theory I have heard about loud music volume, which applies to bars and pubs.
Essentially, on those nights where people are there for conversation, social enjoyment etc. as well as live music, loud volume means people have to shout to be heard by the person next to them. Sooner or later the throat starts to get dry (helped along by cigarette smoke) necessitating its irrigation by alcoholic beverages.
Loud music thus helps the bar sell far more beer than quiet music.
I wouldn't be surprised if venue owners haven't over the years encouraged increasingly high volumes through PAs. Certainly, I know one local bar where the manager is always helpfully fiddling with the sound board.