The reason is this changes are not aimed on average Joe developer writing C# microservices. This changes and whole Span/ref dialect of C# are aimed on Dr. Smartass developer writing C# high performance libraries. It's advance-level feature.
Basically gives you a release-by-release highlight reel of what's changed and why it's changed.
I glance at it every release cycle to get an idea of what's coming up. The even numbered releases are LTS releases while the odd numbered releases (like the forthcoming 9) are short term. But the language and runtime are fairly stable now after the .NET Framework -> .NET Core turbulence and now runtime upgrades are mostly just changing a value in a file to select your target language and runtime version.
https://learn.microsoft.com/en-us/archive/msdn-magazine/2018...
Span makes working with large buffers easier for Joe developer, if he could be bothered to spend 20 seconds looking at the examples in the documentation.
But before span and friends you could always use pointers. Spans just make things friendlier.
And C# also has built-in SIMD libraries if you need to do some high performance arithmetic stuff.
My assumption is since there is a GC, and it is not native code, there are too many use cases where it can't apply, but rust can. Once there is a way to have it compete with rust in every use case rust can be used, maybe there will be more talk.
The "advanced" stuff is very much about bringing Rust-like lifetimes to the language and moving the powers and capabilities outside of the `unsafe` keyword world, by making it much less unsafe in similar ways to how Rust does lifetime/borrow-checking but converted to C#/CLR's classic type system. It's adding the "too clever" memory model of Rust to the much simpler memory model of a GC. (GCs are a very simple memory model invented ~70 years ago.)