PWA's are great when they're available and work. Many devices/browsers don't support them fully yet though (or in a usable form) and they're still a bit tough to get right for the average dev. I got frustrated for an embarrassingly long time learning ServiceWorkers.
As far as Netflix.com becoming a PWA, it might happen at some point, just not yet. e.g. iOS Safari is DOA because no ServiceWorkers and no Encrypted Media Extensions. Their "save to home" UX isn't yet as seamless as Android's. I'm not on the team responsible, so I don't want to speculate too specifically! :o)