I hear this phrase all the time. What does one do at a bar? Why do so many people go there?
If you don't go, why do you care?
You drink, you talk to people, sometimes you dance, sometimes you go home with someone you didn't come in with, sometimes you're there with friends, most likely you will have to pee at some point, you flirt with the bartender who could care less.
You will also pay too much for drinks.
One finds a change of pace, a change of scenery. One is drawn outside of ones' normal routine perhaps to share a laugh and good cheer.