But aren't they pricing based on how much it costs to show the film?

Which in turn is how much the studios and distributors pay to make/market the film?

Which is in turn driven by costs...

Which are basically large bets on if a piece of art will have mass appeal.

It makes no sense from a classical economics perspective to keep the theater empty. Even if no one is buying at the break-even price, it can make sense to sell below cost just to recoup some of the investment - and adjust the investment in the future, of course.

Now, in reality there are second-hand effects, of course - like people getting adjusted to the below-cost ticket prices and being even less incentivized to buy at the normal price.

I used to work at a VUE, my flatmate was a manager. I always complained about the awful, awful films we showed with no one watching them. Surely it'd be better to show some classics that would sell?

Apparently the deal back then was that theatres had to buy films in packages. If you wanted the latest blockbuster, you had to buy a bunch of terrible dross, and commit to showing it X times.

They should price to get the most profit (or least loss). If people would buy tickets regardless of price, they could set them at $1 million each.