Maybe I am the misfit. However, when I play pool in such an establishment I usually eat a hamburger and throw back two or three or four brewskis.
Then you are a better 'pool player' customer than most.
As for who stays open and for what reasons, I can't honestly say I know the answer to your question. What I can tell you though is that not infrequently at Chris's Billiards in Chicago, where they have no specials, but do have pretty reasonable rates, in the $3 an hour range, which vary according to the time and day, I play there late into the evenings/early morning hours/til they close, and they aren't complaining.
plenty of customers (players and the retail crowd) will always keep a room open and doing well
If the pool room/bar owners aren't able to do the specials, that's their call. However, when the rates get too steep, I'm elsewhere.
I've seen rooms that would rather adjust their opening times from 10-11am to 4pm rather than pay for staff and operating expenses. no customers, no reason to be open at that time... there is always a 'break even point' when that is not reached, time for changes.
Flex