You have to put yourself into the head of a bar owner, she or he wants people to order drinks, talk to other people, meet someone, dance and so on. If the band takes over the decibel levels in that space, some or all of the other parts will suffer. Worst, there are people who don't like loud music so they avoid the place, too.
It's Ok to play loud in concerts, that's another story. As for bars, someone doing that will just minimize their chances for more gigs in bars in future.
Personally, I guess I'm getting old but nowadays I rather like to hear musicians play in my ears than *feel* them play in my stomach.