How does Netflix monetize this??

All of their movies are monetized the same way. Through subscriptions.

Some people most definitely do that. But netflix knows everything people do on their service. If someone signs up for the free month, only watches that film and cancels before the end of the month, they know that. That number is very small. More likely than not, the typical user will browse or search around. And based on that relatively small amount of data, Netflix will serve them choices that have a high probability of being watched by the user. That is their whole model. Keep serving them things they will watch, make it worth it for them to pay the next month.