Earlier quoted context omitted.
The marginal cost to serve you more videos is real, but it’s negligible compared to the fixed costs or cost of people not re-subscribing. So I assume that people at Netflix were optimizing for usage/engagement just like the ad driven services as a proxy for subscribe rate.
This is the correct answer. The more you watch, the less likely you are to unsubscribe. If you haven't watched a streamer in a couple of months, that's the first thing you'll cancel when you glance at your credit card statement.
Of course with their ad supported tier they probably don't agree.