Um, except that they are all in the same theatre?
The theatre owner doesn't give a damn what you watch, as long as you're watching something and buying $10 popcorn.
In other words, blockbuster hits entice you to enter the theatre, his job is to make you stay. If he fills up all his theatres with non-customers paying $3, he is unable to achieve this task. Knowing that it is extremely rare for you to make it to the theatre and not see a movie, there is no incentive for him to offer any lower prices.
If you make it to the theatre, the sale is but guaranteed. Lowering prices after the sale is guaranteed is a stupid way to do business.