I think the value-add of 'you can go to any theater' is a tough sell. If the theater that I frequent offered a subscription that was any amount less than MP I would probably switch. Why would I drive further to see a movie?
If I have a MoviePass I can go to any theatre. That means I can go watch a movie with my friend who lives in the Bay area, or my Grandmother who lives in Arizona. Your question, "Why would I drive further to see a movie?" is exactly why multi-chain subscription is superior. Because I don't always go to one theatre in one city.