I'm convinced that they do it to get you out faster. The quicker they can turn you around the more money they make. Who wants lo linger over a cup of coffee or sit and have a conversation when they're being treated to 140 decibels?
I’ve heard that said, and it could be right. On the other hand, you’re more likely to pay for a dessert or more beer if you’re not in a hurry to get back to the peace and quiet of your child-filled home.
My alternate theory is that the people working in many restaurants have had loud music turned on constantly since they were young children. They can’t imagine people’s wanting to just talk to one another (that’s why there are all the televisions in the restaurant, too), and their hearing is damaged so that they don’t know how loud it is to people who can actually hear.