It’s in many ways similar to the way the early web was developed, different browsers tried out many different additions, copied the better ones and improved them. The standardisation process we now have didn’t exist back then, and has been through a number of iterations itself since (the “xml every thing” process that ended with xhtml had a questionable outcome at best).

Some may argue that a formal standardisation process should have started earlier, before IE became too dominant. But I’m not too sure, IE was incredibly innovative and introduced some important technologies and apis, before stagnating.

In fact the “modern” html/css/js standardisation process is specifically lead by individual browsers implementing and trying out new additions, with formal acceptance dependent on other browsers also implementing it. It’s inherently a implementation lead standardisation process, not necessarily committee led.