There was this idea that if you had all movies available the long tail (obscure, old etc movies) would still be watched by at least some people, but in practice most people just stick to what's new/mainstream/known, so that it's not worth the extra hassle to maintain a long tail library.

Tons of tracks on online music stores for example are never streamed or only a handful of times.

(Of course the limited stuff e.g. Netflix has, is by no means not even the 10% of possible content).

But even if so, can those few not sufficiently monetize things to warrant the storage and delivery costs? I mean, yeah, old movies once had their original film melted down, but for the past 80 years they've at least thrown it into a vault or similar. Physical storage is orders of magnitudes more expensive than digital; even just dropping these things into an S3 bucket and serving them as needed for .10 cents would cost less than what they used to do, -and- would allow them to actually make money from it (albeit very little).

If you don't want -any- of that, then why not release it for free and allow things like the internet archive to store it and deliver it for you? It's worth the money to store it -in case- you want to do something with it, but not worth the money to actually do something with it, even though that costs no more and has a return on investment?