Given that the ECMAScript community has (for good reason; "don't break the web") decided to avoid backwards-incompatible changes, that necessarily places a limit on the amount of "fixing" they can do to the language. New or enhanced features are okay, rectifying mistakes is harder.
(This isn't just a JS thing; go talk to any random Python developer and ask them what they think of Python 2 vs 3. There are tradeoffs to both approaches.)