One thing this doesn't do is take into account the size of the bars in question. When I visit Minnesota there are little Mom & Pop bars everywhere (thank you German immigrants) with a dozen seats and maybe a pool table. Meanwhile down here we don't have many bars, but the ones we do have are usually full on enormous nightclubs that hold several hundred people. The only smaller bars around here are the ones in Hotels.
I suspect blue laws could play a big part in this. If you live in a drier area where liquor licenses are expensive, strictly limited, and hard to get, then small Mom & Pop bars don't make much sense. Also, in my state you can't serve alcohol at all unless you also serve food, so technically everything has to be a restaurant, which increases the cost of entry as well. I suspect that graph would look quite different if they included "restaurants that have a bar in them" in the list.