While you watch Netflix, you don't watch a competitor. In a way, this autoplay feature removes a friction for the customer that doesn't have to decide what to watch next. This removes the "danger" that the customer think about that cool show that is not provided by Netflix.

At the end of the month, the customer may think about how much they use a TV provider and not the other, and decide to keep Netflix and ditch any other subscription they may have.

It's true that it burns through Netflix content but they made 1,500 hours of original content in 2018, content that they have to create anyway for other reasons, so a lot of your free time is already covered.