No doubt the licensing and contractual issues are a thorny problem, but the licensing and contractual issues are generally from the studios who created them. If they wanted they'd be able to get around it, or find a compromise or similar.
There is absolutely no excuse for not having a cheap platform streaming every pre-2000 movie, except pure greed from the copyright mafia.
I'm not so sure about that. The movie business is notoriously crappy - most movies never recoup their costs. It's the few wild successes that keep the studios afloat.
On the other it is true that the marginal cost of selling digital downloads of back catalogue movies is close to zero.