It's a very slippery path towards per-watch pricing with "rent this episode for just $0.99"... and that will be horrible.
Largely this breaks down into two salient factors:
- the friction of the transaction itself, which you largely shed when the consumer already has already agreed to be billed on usage, and
- metering aversion, which can be alleviated with a wide range of cheap tricks, e.g. using very coarse quantization: think not "rent this episode for just $0.99", but "rent up to 50 episodes this month for just $9.99". But the extreme of this is what you actually see: one price for any usage of the service at all, which ... is a popular pricing model at consumer scales because it works?