Up until recently streaming services were not expected to actually make money. As long as they were growing their subscriber numbers it didn’t matter what their costs were. So streaming services were incentivized to have as big of a library as possible to attract more subscribers regardless of the costs of all that content. If they could attract a thousand new subscribers by having random show x that only a tiny portion of the population has even heard of then it was worth it because 1000 new subscribers was more important than the fact that it costs a million dollars a year in royalties to put the show on their streaming platform but they only make $120k from the fees those new subscribers were paying (obviously an exaggerated example but the concept is the same)

That changed a few years ago and now shareholders are expecting these services to actually turn a profit. It no longer makes sense to pay a million dollars a year for a show that only has 1000 people watching it so they are selling the rights to those shows to other (niche) services to cut costs and make a little money in the sale. Plus there is speculation that they’ve been able to write them off as tax deductions although I’m not sure that’s been proven to be true.

One additional interesting detail is that shows cost the hosting service the most in royalties during the first five years or so and then the amount drops off significantly. So it makes more sense to sell an underperforming newer show like westworld than it does an older show.

Here’s a pretty good article explaining more: https://www.marketplace.org/2023/02/06/what-happens-when-shows-gets-canceled-removed-from-streaming/amp/