The family of 7 also doesn't pay less.
So is this specific movie "$30" more valuable than any free alternative? Or is it the "newness" you are paying for? Have you7 watched all other movies worth watching already?
I would guess that people are (or were) paying extra to go to a theater because of the spectacular large screen and the experience in general. One feature of going to a theater is that you have to watch the movie in one sitting and there are no ad-breaks. That can add to the totality of the experience. And it's fun to get out of your house and to do that you need a reason .
That sounds like a very poor cost/value.
A sporting event, visit to a zoo offers so much more at that price point.
And matinee is cheap because it's an inconvenient time.
Also, $5 snacks sounds like the cheapest snack they had. If you bought popcorn, it started at $6 or $8 for the small, even in middle GA.