The vaccines aren't 100% effective. In the last couple of days infectious disease experts have been coming on CNN and MSNBC and stating that achieving herd immunity in the entire U.S. will be impossible this year and possibly next year also. Maybe if the vaccination passport is required for everyone (and strictly enforced) in a theater, mask-wearing might be optional. We'll have to wait and see. Lately the number of deaths per day has averaged 715, although on May 3 it was 460.
I came down with covid in late January and got through it and was vaccinated with the Moderna in February and March. I've been going to local movie theaters since mid-March. I've kept my mask on throughout the movie except when munching popcorn. I've gotten use to it, although obviously I'm not crazy about it. I've seen around 10 movies in the last month and a half. Generally there have only been about 5 other people in the theater with me. However, when I saw Judas and the Black Messiah a couple of weeks ago, there were probably close to 40 in the theater, although none anywhere near me.