> What is going on?

The copyright owners of movies with know stars from the 1960s have their own platforms and aren't licensing the movies to Netflix.

Hence, why Netflix has for years been making a huge original-contenr push; once it proved out streaming as a business model with other people's content, getting (or keeping) such content became more difficult.

I think the immediate reason why a lot of the older movies are not coming back is partly due to a rights management thing (films are usually negotiated for terms of n months/years, and renewing the contracts is a cost), but also they impact the size of CDN working set. The "long tail" where 90% of traffic is accessing only 10% of the files kept on origin makes for an inefficient proposition for an SVOD service. This is even more of a pressure when you are both the VOD service AND the CDN. I suspect Netflix spends a lot of man hours finding which titles perform in consistent viewership and prioritise those for the reasons above - besides, how many times can a person watch Breakfast at Tiffany's per month?

Netflix's data suggests those films won't be viewed enough to be worth buying.