[anjc]

> They act as if they are paid by amount of time you spend watching movies

At least up until 2015 (last published paper that I'm aware of) this actually is how they optimised their recommender:

"However, we have observed that improving engagement—the time that our members spend viewing Netflix content—is strongly correlated with improving retention. Accordingly, we design randomized, controlled experiments, often called A/B tests, to compare the medium-term engagement with Netflix along with member cancellation rates across algorithm variants"

Gomez-Uribe, C. A., & Hunt, N. (2015). The netflix recommender system: Algorithms, business value, and innovation. ACM Transactions on Management Information Systems (TMIS), 6(4), 1-19.

It's probably a reasonable approach and has clearly been successful