Many rooms do have tournaments. The ones I participate in mainly draw in people for the tournament and are nice ways for the locals to compete in a handicapped format without really paying too much. When I first started playing, the tournaments were the only competition I has (since I was too young for a bar league) and gambling wasn't really an option (since I had limited income). I would go in multiple times a week to practice since I had something to look forward to. Tournaments bring in players which is important and also help some to keep an interest in the game, in this sense the actual tournament can be seen as a loss while a net gain can be seen from increased player interest.
I'd imagine it's a different story in a bar where the primary product is alcohol and pool just brings people in.
Also, how the tournament is run affects the profitability. If all entry fees and greens fees are paid to the field, then of course the profit is a bit lower. Balancing these types of variables are difficult when you're looking at a smaller tournament with a limited number of people and a low entry fee.
