> I've been kind of puzzled, since the first time I gave it any thought, why "going to a movie" is culturally thought of as an activity one does with a companion, even a date.

Because after going to the movie, you've all seen it, and so can talk about it with each other.

> spend maybe 5-10 minutes critiquing or raving as you walk out.

It's not just for that trip, but it'll be a shared touchpoint. And if it's something you really enjoyed, it's something you'll be able to talk about together for years—like going to see Star Wars as a kid.