Since the eighties, the game is played that if sales go down, raise prices to "keep a steady cash flow".
It's called whatever the market will bear, and it's a basic tenet of capitalism. If you charge too much eventually people find an alternative, or they die or riot or something, so charging the maximum amount you can while maintaining a kind of stasis is the universal goal. It's not setting the highest price people will pay today, it's setting the highest price they will pay today and then come back and give you more money tomorrow.
I don't know if the price points now are optimal, but a lot of the people priced out of going to the movies probably aren't profitable customers anyway. They sneak in snacks instead of buying them, and the snacks are where the big profit comes from while the ticket price generally covers little more than the film itself.