For the first few weeks of a film's release, all of the ticket sales goes to the studio. Pretty much the only revenue for the theatre is popcorn, candy and soda.

Since most theatres have gone full digital, the "projector" won't show the film if there have been no tickets sold. That eliminated the game of buying one ticket and then sneaking in to see a few more movies.

How much extra does it cost to show an extra movie that nobody shows up to? It seems like the majority of the cost is rent of the building and salary. If employees are already working to operate the few movies that are expected to have people and the building is already being paid for then they may as well use up all their theaters just in case since the extra cost would be low.