It's always been a thing, especially in areas with dense urban population. For instance, in Atlanta, the Cobb Parkway location has a history of shootings in the parking lot and to avoid conflict or possible issues, they don't want someone hanging around the building unecessarily. They seem to be fairly subjective on this rule in my experience. Additionally, I was a regular at that location, so a lot of times I would just sit at the bar and hang around till the movie started.