With the Advent of reserved seating I don't get why this is an issue anymore. Buy the seat you want, let the companies buying ads subsidize your ticket price, and show up after they've played. There's no reason anymore to be stuck in your seat for 20 minutes before show time.
Because you dodn't actually know when "showtime" is. I've never seen a ticket that listed the amount of time the commercials were going to take so I'd know when to be there. Ticket says 5:00, but actual movie didn't start until 5:37.
My local theater:
Ticket window opens 10 minutes before the start time.
Cash only.
No reserved seating.
No commercials. It's a blank screen until the trailers start.
We get two new first run movies a week to choose from.
I think the regular ticket price is $7. We always go during matinee so it's only $5.
Going to my local theater is like walking into the past where everything except the movie showing is a throwback to the 80s.
Don't assume all theaters have reserved seating or any other modem thing.