There's also a big psychological difference between deciding just the once to start a subscription, and having to constantly decide if you want to pay to watch

There's also a big psychological difference between deciding just the once to start a subscription, and having to constantly decide if you want to pay to watch a particular series. Even if the prices worked out similar, I think people would be less likely to watch if they had to decide to spend 50c (or whatever) each time they watched an episode.