Free plans don't work when the cost of providing a service is high. Google, Facebook and the like can happily give away their products for free and lose money on the bottom N% of users, because it still amounts to pennies. Netflix has high bandwidth and content licensing costs that scale per user, so they need some barrier to entry.
Could they offset bandwidth by using torrents? I mean, it works for the pirates, even though there is no way to enforce people keep seeding (apart from private trackers maybe).
They already do something similar called open connect https://openconnect.netflix.com/en/
I am pretty sure the biggest cost is licensing. Also why you see Netflix producing so much original content.
