Drives me crazy that they do this. Take Pay-Per-View for example. Why is it that on demand services like Vudu don't have the ENTIRE library of movies? Why not?

Drives me crazy that they do this. Take Pay-Per-View for example. Why is it that on demand services like Vudu don't have the ENTIRE library of movies? Why not? Why would a movie not be on there? Because greed. Because Vudu won't charge $5 for a classic movie but the studio wants to charge more than a bargain bin for a 24-hour rental for some reason. Or maybe it's some lame reason like pride.