Well if you think about it, the netflix UI is pretty much a bunch of documents. It's a gallery of images, and each image has its own document.

The DOM is a dinosaur unfortunately, it just gets the job done for most basic websites. CSS is also a language made for the DOM. The thing is, the DOM isn't required for a web page. Netflix could have coded up their entire UI on a Javascript 2D game engine and could have ended up with a faster app for sure. But CSS and the DOM make it much easier to work with text + links, that imo it's worth it for the performance drop of animations.