I was under the impression movies were distributed on encrypted physical media which the key was made available on the release date. Maybe things have changed.
I recently went to a small theater to watch a movie. It didn't start. After 10 minutes I went to talk to a manager. They had forgotten to download the licensed movie for the day and that download would take a couple hours. I had to get free passes to come back another time.
edit: A normal DCP (digital cinema package) is around 100GB, bigger if it's 3D/4K/Atmos. Some of the biggest packages can be 500-600GB with all versions (2D, 3D, dubbed, hard of hearing, atmos, auro, DBOX and so on). So not really feasible to download that via the Internet in a couple of hours.