"Dive bars" have always been popular.
A friend of mine in college opened a dive bar, which quickly became very very popular. This was the type of place where you could smell the ammonia from the urinal when you walked in the door. Spending more than an hour in there, and you left smelling like cigarette smoke and stale beer.
When opening his 2nd bar, he made the rookie mistake of "trying to finally do it right". His new bar was walking distance from the original, and had a beautiful wood bar, leather chairs, fancy plate glass windows with frosted lettering, etc (top notch plumbing too).
His 2nd bar never caught on and he eventually had to close.
The importance of "dive's" is that everyone feels comfortable. You feel you can do no wrong. Spill your beer...so what. Whereas if the place it too fancy, everyone becomes too self-aware.
These types of places like BdB aren't about customers "looking down" on the place, its about being in a place thats comfortable and where the average joe doesn't feel looked down upon.