Instead of $10 a month think of it as $120 a year. If a theater charges $12 a ticket (just to pull a round yet realistic number that means less than a movie a month at $10/month) then an annualized MoviePass subscription breaks even at 10 tickets per year.
As somebody who likes to go to the movies, how many times did you go to a theater this year, really? Six, seven times maybe? Maybe once in the late winter or spring, two or three times in the summer, once in the fall, whatever Star Wars movie comes out in the winter, maybe another time with your family during the holidays?
The truth is that people don't really change their media consumption habits, in aggregate, when they're presented with unlimited subscriptions. People just like to feel like they could get anything they want and that they don't have to look at the price tag anymore, but they don't actually consume more in aggregate. Sure, you get some binge subscribers who exploit the system, but they're not enough to bring down the entire enterprise.
If the industry could transition from $10/album to $10/month unlimited music subscriptions, from $10 eBooks to $10/month Kindle Unlimited eBook subscriptions, from $10 DVDs (actually, usually more than that) to $10/month Netflix subscriptions, then why can't the industry support a transition from $10 movie tickets to $10/month theater subscriptions?