I agree that the risk level is above a lot of other activities, but I sit in an office daily with other non-mask wearing people, I visit various stores while wearing a mask, and do various outdoor activities with no mask. We take sensible precautions such as avoiding crowded stores, doing grocery pick up and only going in during odd hours when the store isn't crowded, and do not have contact with persons who have had even 2nd level contact with anyone showing symptoms of anything. We have no contact with at-risk persons, and no one we have direct contact with (close family) has contact with at-risk individuals.
I guess what I'm getting at is that for a lot of people, myself included, a socially distanced movie theatre lines up with an acceptable level of risk. A level of risk that my life is already at, and that we as a family deem a balance between full quarantine and 2019 lifestyle.
To keep the thread on track, I believe theatres are depending on persons in my demographic to attend and are in general doing what they can to maintain revenue and even if not operating in the black, operate at the smallest red number possible. Its certainly not a perfect solution for any party, but it seems to be working at some level. And because of the risk you mentioned I believe that Theatres will continue socially distancing and mask policy well into 2021, even after some other industries may have moved on.