How does assigned seating confuse people?
You arrive and ask them to move, they apologize and say “oh but my friend is here, I see some empty seats up there you could take instead!”
So you go sit in those empty seats, hesitantly. Then someone comes in and tells you that you’re in their seat. You try to explain the situation but…
Etc etc etc.
This has happened to me multiple times on long-distance transit before (bus/train), it ends up being chaos if just a few people don’t perfectly follow the assignments.
The time I saw it, it wasn't at the seats like the other comments are suggesting. It was at the ticket line, an old couple who didn't understand why they had to pick a seat, or what the screen in front of them represented, or something like that. I don't remember how that was resolved but they did end up getting a ticket and going in. After seeing that I'm assuming there were people who didn't bother and went somewhere else.
I also am quite late in many situations, but in a theather you just go, if you can manage to be seated, before it gets dark. Everything else is just rude.
For live plays, with assigned seats and no captive marketing, people do come on time generally.