There is no conspiracy - theaters will just straight up admit that the prices of soda, popcorn, and candy are what they are because they make (at best) pennies on each ticket sold and make up for that by making a high margin on concessions.
I didn't say otherwise. My theory is just that some foods are more vs less conducive to policing, and theaters benefit from a strong preference for one particularly easily-policed food. That goes beyond the general economic logic of concessions markets that you repeated here.
