They're open pretty much all the time and don't close at night, so naturally drunks and other rowdy folk congregate there. Prime time for fights to break out over silly minor things, which often turn physical. There's a reason most restaurants shut their dining rooms down by midnight.
In New Jersey we have 24/7 diners. You can get breakfast or a burger, or whatever you want basically. Don't knock a 2 AM drunken pancake until you've tried it!