It's about volume. Sure the movie companies will be giving away their films for free. But if you give away enough films for free it becomes profitable!!
Amazon actually shifted the pricing on books and e-books by selling them at below what they were buying them at for prolonged periods of times, and drove rival book sellers out of business by doing so... and then didn't raise their prices.
http://www.slate.com/content/dam/slate/blogs/future_tense/20...