If they only wanted to consume the content, they could wait for it to hit video
Not so. The "big screen" (bigger than the biggest TV) is one of the appeals, is it not?
Solely to grief people with your device?
You see, developmentally delayed types like you consider brief and very infrequent checking of a phone without talking to be intolerable. It's unfortunate that you cannot focus your attention. You are free to attend your bizarre members club.
I don't need it, because I don't have a taste for adolescent films while hating adolescents.
It might be that the only way to guarantee to stop excessive use is to prevent all use.
I haven't really ever been annoyed by phones in a cinema, ever.
We might also be generally more polite in my part of the world, with less need for the cinema equivalent of the gated community.
FYI, I always turn a phone off when I go to the cinema, but there are myriad reasons why someone might need an alert. On vibrate, of course.