The details are important, and running a good CDN isn't easy but....it's a CDN serving files. People really did build a completely free version on their own time [1]. That also costs less to run (kind of a requirement if you're building a BitTorrent streaming client).
It's important to think really carefully about what Netflix actually does, as opposed to what they like to pretend they do: because all the important stuff isn't really tech, it's business, bureaucracy and manual labor - subtitling, license management, ISP negotiations for server placement, someone going through every episode of a show to set the "skip credits" titling.
Streaming sites are “good enough” now and will live:die on content.
I honestly have no idea what all that engineering talent is doing such that HBO Max is able to replicate 95% of the technology experience.