I also wonder that. IE is famously non-compliant when it comes to web standards and they were a big player back then.
Chrome gained a lot of it's early traction by being quick to adopt new technologies.
I wonder if it was also to do with the dramatic increate in the size of the spec. ES4 would have added so many more concepts I can't help but think thebrowsers would have nather not gone to all the effort.
It's safe to guess that if Netscape had won in the 90s, JS and the browser would have progressed much farther in the 2000s. Microsoft was in it to stop the browser being used as a platform that threatened their monopoly. Once everyone was using IE, they had little incentive need to improve it.
Chrome gained a lot of it's early traction by being quick to adopt new technologies.
I wonder if it was also to do with the dramatic increate in the size of the spec. ES4 would have added so many more concepts I can't help but think thebrowsers would have nather not gone to all the effort.