Ferrous Systems donated their language specification ("Ferrocene") to the Rust foundation[0] who is working on integrating it but that takes time, obviously.
0: https://rustfoundation.org/media/ferrous-systems-donates-fer...
0: https://rustfoundation.org/media/ferrous-systems-donates-fer...
Do you think that it was made up from whole cloth in the abstract machine and implemented later? No, it was based on the available implementations of its time.
On top of that, languages like Python do not have a specification and yet have multiple implementations.