Well almost all the JavaScript language innovation was syntax sugar and was implemented as transforms before the browsers implemented it. I think JavaScript devs mostly were fine to keep using transforms indefinitely and it's just been more convenient that the browsers have moved to implement it.
Python could have done this easily too but evolving as a language just isn't as big a priority (not that I'm saying it should be) and that's completely (or mostly) disconnected from their backend implementation decisions.
