One real danger of putting all historical video media on streaming sites is that it makes it far too easy to introduce an Orwellian Ministry of Truth that is empowered to rewrite the past to make it conform to today's acceptable social norms, academic ideologies, government agendas and so on.
For example, one could make the argument that Alfred Hitchcock's entire library promotes negative stereotypes of women - and it's true, women in Hitchcock films are not the strong types, they're more often helpless victims who have to be rescued by male characters. This clearly, one could say, promotes negative female stereotypes which are damaging to young women so all those movies should be removed from streaming services.
One could continue in this manner, selectively pulling anime movies because they promote excessive violence and sexuality to a teenage audience, or war movies like Apocalypse Now and Dr Strangelove that portray military generals as clueless maniacs, or if the pendulum swings back to the social conservative end, pulling all horror movies that don't portray Christianity in a positive light or have too many Satanic themes, and on and on.
Keeping hard copies in your personal possession is one way around this, but since the copyrights and hence distribution rights are held by these conglomerates that don't want to get in trouble with some political group or other by making them available, nobody else can view them without going through pirate sites - a very unfortunate situation.