Walmart’s not going to be a good model, there, as while the chance of abuse being the cause might not be 100%, it hangs out near enough 100 to know more than a few intimate things about it.
If you’re asking someone to collect your groceries, maybe pay them to do so. Tips are broken as a concept, so whatever there.
Unfortunately they’re trapped. If they lowered the price of food and raised the price of admission to compensate people wouldn’t notice. In fact, they wouldn’t even make it to the food to see, they’d just know that one cinema has $10 admission and the other has $20.
They could advertise that they have lower concession cost to attract people, but there would be enough people thinking “I’ll just go to the cheap one and bring my own food/not buy food.” that momentum wouldn’t move into their favor.