where there’s demand, they still let you become its permanent owner. (

this is not true. in-fact it is seen as a marketing tool for the subscription services. market-forces do not naturally lead to the outcome you are describing.

it is also not the “exception” that something isn’t available, it’s an exception when a subscription service does release a purchasable option.

Indeed it’s getting more and more common that not only will shows/movies be unavailable for purchase, but deleted from the subscriptions too.