What Gwen is encountering with streaming is the standard risk be it streaming from Amazon, Hulu, Apple, Netflix etc:

You are at the mercy of the streaming provider in what is made available.

The traditional alternative is to buy the media but with people voting with their wallets and opting for streaming, the production of media is in jeopardy, or if available, is much more costly as there is less economies of scale which means less people will buy as it makes streaming seem less costly etc.

Honestly it is a bit of a death spiral. Media is more resilient as the resolution goes up and up due to needing much higher bandwidth, bandwidth that may be constrained arbitrarily by the likes of Comcast.

However, most older content (say older TV shows) is still on DVD as it is cheaper to produce.

Anyway, even holiday staple movies seem to have disappeared even from cable due to them getting owned by other companies who only want them streamed. More and more, those movies no longer appear even on Blu-Ray. Alistair Sim's 'A Christmas Carol' is a prime example of it being no longer available in Blu-Ray and I did not recall it appearing on Cable either.

If you like a movie, and you want to watch them whenever the mood strikes, I would suggest that one should buy them now on physical media else it may or may not stay available going forward.