[superme]

They do it on purpose. The less patrons talk to each other the more alcohol they drink. That's why the music volume is increased as the night progresses. They get them into the establishment, customers start drinking, eventually it gets to a point where they can't hear each other so they just focus on drinking. Not all places do this, just the places that are strongly focused on the profits.

[sukilot]

Why would such a bar have any repeat customers? The music is loud at a bar because the people are loud because the bar is crowded.

If bars wanted to sell more drinks, they would have more bartenders to reduce the wait times.

[superme]

There you go: http://www.theguardian.com/science/2008/jul/19/medicalresear...

It mainly happens in busy city bars/pubs, where repeat customers aren't so important.