Craft beers are cheaper for restaurants and have a higher profit margin, and there's the "community" factor of having local brews; and in some cases just some "good ole boy" attitude. There are a lot of incentives. It has not much to do with net sales, because it is offset by other incentives. Customers don't often complain, especially in bars that are for partying and generally just getting drunk. Who cares if this local brew tap doesn't get much requests? There is no feedback, and it just drives the people who like "imports" to buy bottles and the profit margin is even HIGHER there. It's a win/win for the restaurant/bar.
That's not always the case, there may be a short term gain, but long term it may hurt sales as people go to different bars with more imports on tap. Here in Nashville there has been an influx of beer halls that serve German and Belgian beers, imo as a backlash to the localization of beers.
