It only became legal in New York in 2022. Perhaps today most people in the US do live in states where it is legal, but that doesn’t mean they live near a theater that actually does it. This article from a year ago says the largest chain, AMC, has a bar in the lobby of 300 (of their 593 in the US, according to wikipedia) locations but that some of them don’t let you bring a beer into the theater. The second-largest chain, Regal Cinemas, was only serving alcohol in 80 of their 511 locations as of last year.