Great question — answering as the UphillTech team:
The offering of a show(s) (entire series or particular episodes) and movie(s) for streaming is governed by specific licensing deal ( distribution rights ) with the content providers, be it a channel (in case of series) or a production house/studio (in case of movies). Netflix enters into agreement with the content providers which have specific clauses about availability of a content through different mediums (Disc/Streaming), along with time period, for which the agreement stands valid. The content providers can enter into agreements of varying nature for different content - some content might be available for short period of time, after a certain cooling period (Netflix can offer a certain...
Full answer by Incognito: https://movies.stackexchange.com/a/9824 (CC BY-SA 3.0).
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