This. While yes, it was a long way from "standardised" and a lot changed between what Google initially published and the Ecma standard, many fundamental design decisions were made internally and there was never any real influence externally over that. Those are fundamental design decisions where to change them you essentially need to start from scratch.

The other big problem was that it was done with the VM being a major part of the project with the intent of getting it into Chrome, obviously without having talked that much with several of the people who have significant influence over such things in (then) WebKit, even those within Google. That the VM was going to be outright objected was entirely predictable.