What is so facinating about closing time?

We close our office and store at 10PM. After about 8PM it slows down, save for the late check ins. After about 9:30PM we start cleaning, vacuuming and getting things in line for the next day, since the office and store is a ghost town. Then at 9:55 you can almost count on one or two groups to come in, wander around the store aimlessly, picking up and examining every item in the store, not taking any hints that we may be ready to close, such as us turning off the display lights, putting the covers over the computer terminals etc. They will inevitably stay until about 10:15 and then mosey on out without making so much as a ten cent purchase. I know this is common throughout all retail and extends into the dining industry as well. I have a good friend who owns a high end restaurant, and he has the same experience, some diner will linger for an hour after closing and finishing their meals, not ordering anything more expensive than a refill of their ice water, oblivious to the employees who would like nothing more than to close up and go home. And to top it off, he says they are always bad tippers, a problem I don't have to worry about. Just what is the big thrill?