LFS is not comparable, you can make your own opinionated choices and so it's feasible to have a small scale linux distro. The web is not like that, there's a massive non-optional spec you must implement for your browser to be minimally useful.. and even once you get there it takes a lot of people to merely maintain that level of completeness and compliance.
The state of web browsers is more comparable to derivative distros like Debian based or red hat based etc. They don't hard fork, they track upstream with a bunch of changes continually rebased on top.
> Searching Google will find a lot of people forking Chromium and adding their own changes.
Those aren't hard forks, they are derivatives, you wont see those people continually extending it with new features from W3, fixing zero days and improving implementations... they are the "debian based" in my analogy.