This right here is extremely frustrating to me. There is approximately zero marginal cost to distribute that back-catalog, but they just keep it locked away. I think Amazon does the best job of the legal sources I have seen, though I find it hard to stomach paying $4 to watch a movie made before my parents were born.
If you don’t want to pay a few dollars to watch a movie and the parent comment finds ridiculous to subscribe to yet another provider, what incentive do they have to make their catalogs available?