“Just” is doing a lot of heavy lifting there. There’s a lot that has to go on between the backend and frontend to make modern websites with all their dynamic moving pieces, tons of video/imagery, and heavy marketing/analytics scripts run on a single thread (yes I’m aware things can load/run on other threads but the main thread is the bottleneck). Browsers are just guessing how it will all come together on every page load using heuristics to orchestrate downloading and running all the resources. Often those heuristics are wrong, but they’re the best you can get when you have such an open ended thing as the web and all the legacy it carries with it

There’s an entire field called web performance engineering, with web performance engineers as a title at many tech companies, because shaving milliseconds here and there is both very difficult but easily pays those salaries at scale

> There’s a lot that has to go on between the backend and frontend to make modern websites with all their dynamic moving pieces, tons of video/imagery, and heavy marketing/analytics scripts run on a single thread

So there's a lot going on...with absolutely terrible sites that do everything they can to be user-hostile? The poor dears! We may need to break out the electron microscope to image the teeny tiny violin I will play for them.

All of that crap is not only unnecessary it's pretty much all under the category of anti-features. It's hard to read shit moving around a page or having a video playing underneath. Giant images and autoplaying video are a waste of my resources on the client side. They drain my battery and eat into my data caps.

The easiest web performance engineering anyone can do is fire any and all marketers, managers, or executives that ask for autoplaying videos and bouncing fade-in star wipe animations as a user scrolls a page.