Because I suspect whatever solution they would come up with will end up being as complex a monstrosity when trying to interoperate with other browsers, other OS, other organisations, other developers, various form factors and devices etc...
Also, if I need to learn a whole new stack to use a whole new product that has no-one using it yet, chances are I won't bother.
We may win on learning from the past and not having some of the tech debt the web has, but I've seen this industry repeating the same mistakes over and over again so I wouldn't bet on it too much.
What i meant is getting rid of html,css,js,etc and the entire stack and replacing it with something simpler. There isn't an issue with interoperability with other browsers as there wont be any other browsers, there is no need to interoperate with other organizations as there wont be any other organizations and any interoperability with operating systems can be addressed by simply using cross platform tech when building the browser.
You may not bother but others will (and really you can say that about anything that tries to come up with something new, that is not a reason to stop trying to come with new stuff).
Yesterday I was making a bunch of joke marketing lines and "Sorry we still use HTML" was one of them.
It's really just a matter of constraining the novelty. We're trying to make some specific improvements on the applications & networking stack of the Web. Redoing the entire web platform is out of scope (for now).
Also, if I need to learn a whole new stack to use a whole new product that has no-one using it yet, chances are I won't bother.
We may win on learning from the past and not having some of the tech debt the web has, but I've seen this industry repeating the same mistakes over and over again so I wouldn't bet on it too much.