For many interested in creating a browser, a new engine is one of the primary reasons for doing so, and so forking or embedding being the only option means that many who would've created a new browser don't, because from their perspective there's no point in a Chrome/Firefox/Safari clone with a slightly different coat of paint.
WebKit at least partially addresses the clone issue, making it easy for developers to write entirely new UI code using their toolkit of choice, but comes with the caveat of not receiving much attention on non-Apple platforms, which is a problem with browser security being so important.
Aside from that, how do you make money on a web browser? Without some kind of payback, it's pretty unlikely a browser project will get funding. Particularly since there are decent browsers on all platforms already.
It's nearly impossible to create one that isn't. Firefox (and Tor) is basically the only one.
The ecosystem is the big issue for a lot of these products. It why Microsoft's Windows phone failed so badly - they didn't have the app store to compete with or allow users to migrate to their platform without losing a lot of apps they already used on Apple or Android.
The ecosystem is a major reason why you don't see more competition.
Opera switched to Chromium because they didn't consider it profitable enough to keep developing their own engine, and laid off a large portion of their browser developers. It was entirely about money and nothing to do with using Chrome extensions.
There are perfectly capable HTML4-level browsers like Dillo, NetSurf, etc. and a bunch of similar projects on GitHub (under elaborate yet non-browser descriptions such as "HTML viewer with CSS support".) If only people would stop drinking the Goog-aid and unnecessarily "app-ifying" sites, maybe we would have more browser diversity... after all, the majority of sites I use are from the "document web" and not the "application web".
Edit: downvoted for talking against Google, interesting...
Sometimes I wonder if the web standards aren't designed specifically to prevent any meaningful competition.
That would be if Google cared for developers/users.
Web standards merely describe the current world of web browsers and attempt to retroactively take credit for it.
I'm not sure I understand what you mean here by "take credit" but, that aside, are you suggesting that it would have been easier for Netscape and Microsoft to cooperate (or for gmail to support both) without some standards?
If we're talking about forking an existing browser, that is doable. But you still need a huge investment to understand, change and extend that code. Once again, browsers are unbelievably complex beasts.
Somewhat related discussion: https://news.ycombinator.com/item?id=23161922
Check out the complexity of ES6. You're gonna need an interpreter for that which performs acceptably well, plus a DOM interface to the rest of the browser. And check out how complex CSS is when it starts interacting with everything. Gotta handle all that too. Along with the basics of HTML structure, and how to interpret horribly broken HTML. And all of those pieces have to work together in realtime for dynamic animation, and do so fast enough for webapps to work and without eating too much of the host system's memory and CPU. And handle the constant addition of new JS APIs and how they have to interact with the host OS. Better be compatible and integrate well with Windows, OS X, and Linux too.
Building a new one from scratch today is pretty comparable to building a new operating system. You'd probably need to coordinate thousands of people working fulltime to get it off the ground. And it's basically impossible to charge any money for it, since all of the tech majors give away fully supported mature browsers for free.
In theory, you can fork an existing browser. But they all move so fast, keeping a fork with any useful changes up to date with the main browser is going to take a significant sized team too.
Microsoft is a tech giant, and even they decided to dump their independent Internet Explorer codebase in favor of using a Chromium fork. Now the only other truly independent browser codebase is Firefox's, and they haven't been doing so great the last few years.
It's probably practically impossible to build a browser that isn't a fork of Chromium these days.
https://drewdevault.com/2020/03/18/Reckless-limitless-scope....
Summary quote:
"It is impossible to:
* Implement the web correctly
* Implement the web securely
* Implement the web at all"