Who is going to put the time in to maintain it if the language is given by the implementation of the language? In the past, people wrote huge specs because you wanted multiple companies to implement compilers for their various computers. Now there's enough centralization that a single implementation of a language can exist. Why spend the time supporting 6 compilers when 99.99% of users will use the big 1 that the core language developers are working on? Labor is a finite resource, and because this requirement is gone the extra work that came with that requirement is discarded as well. If someone was willing to write up a full spec and maintain it for 10 years then I am sure it would be accepted to any open source language, but nobody decides to do that with their free time for some reason.