The problem is not that you cannot write lightweight accessible and beautiful websites, you can. The problem is that this is now all part of the "default web browser" and so many people are taking advantage of its widespread availability to use it without a good reason to. Most commonly fingerprinting, tracking, following corporate dev fads, etc. And because of that it is now borderline impossible to have a decent experience using a lightweight browser because so many websites make crucial use of stuff they should really not. It's possible but it takes time and know-how, personally i don't find it fun enough to invest more time than crafting my ublock whitelists. And this is already more than most people (even people that would be able to do it).