while I can see not wanting to provide a full movie metadata API, having "is this or is this not available on Netflix right now" seems like a really important API to have, one that allows websites people use to browse and find movies to funnel users into Netflix (and seems a natural fit for their very popular affiliate program).
Wouldn't that API use would also funnel users to its competitors in the case that Netflix doesn't offer the movie you were looking for?
I see their API closing as a natural business decision — anticipating a time when streaming services are a commodity and margins are thin on streaming licensed content they don't own. They'll have to compete with something else: their core service, their own content, and their recommendation engine (which I find to be fantastic). A public API fights against the recommendation engine. They want you to sit down and watch Netflix, not a movie in particular.