It enables experts in different areas from different countries to come and work together under a set of specific rules that are much stronger that words written in wikis or repos. It also makes it clear that the language is designed for the long term and is not under the control of a single party (as was the concern about e.g. Mozilla which the Rust community tried so hard to dispel).
It avoids embarrassing transitions like Python's 2->3 or one corporation taking control of a language like Oracle did with Java by simply buying it. It avoids having to watch a language go extinct because its corporate sponsor wishes it so (Objective-C, VB 6) and many other such unpleasantness.
This is partly why this AWS focus is strange to say the least. I would have thought that it's obvious for the Rust community that having one large sponsor is not healthy. This tells me that Rust was never really as independent from Mozilla as claimed and Mozilla refocusing away from it seriously hurt the language.