You have to hand it to Microsoft: It may be the only large software company that doesn't seem susceptible to not-invented-here syndrome.
It's true that Microsoft historically has been an intensely competitive company, often trying to undermine competing technologies, e.g., with "embrace and extend" strategies.
But whenever a competing technology -- whether a language, or a framework, or an application -- gains adoption with developers or users, Microsoft to its credit will follow along, sooner or later, and do the work necessary for making it a first-class citizen on Windows.
(For those who don't know, Rust is originally a Mozilla project.)
As much as I appreciate what Microsoft is doing here, your NIH praise is not entirely well targeted - look at this research project from Microsoft, which aims to build a slightly different Rust. https://github.com/microsoft/verona