>why "going to a movie" is culturally thought of as an activity one does with a companion, even a date. Much like dining out in a sit-down restaurant.

Let me unpack a little bit.

I very rarely go to movies and really haven't for years. So it isn't a social activity so mostly won't except for the odd shoe in IMAX.

I will go see live theatre with someone or maybe a group. But am also perfectly happy to do so on my own.

As to meals? I'm so inured to solo meals with business travel I don't think twice. Enjoy eating with friend(s) whether in a business or purely social context. But it's not like I'm going to order room service or go to McDonalds if I don't have anyone to sit with.