Because Anders Hejlsberg is one of the greatest language architects and the C# team are continuing that tradition.
The only grudge I have against them is they promised us discriminated unions since forever and they are still discussing how to implement it. I think that is the greatest feature C# is missing.
For the rest C# is mostly perfect. It has a good blend of functional and OOP, you can do both low level and high level code. You can target both the VM or the bare hardware. You can write all types of code beside system programming (due to the garbage collector). But you can do web backend, web front-end, services, desktop, mobile apps, microcontroller stuff, games and all else. It has very good libraries and frameworks for whatever you need. The experience with Visual Studio is stellar.
And the community is great. And for most domains there is generally only one library or framework everybody uses so you not only don't have to ask what to use for a new feature or project, but you also find very good examples and help if you need.
It feels like a better, more strait trough version of Java, less verbose and less boiler plate-y. So that's why .NET didn't need its own Kotlin.
Sure, it can't meet the speed of Rust or C# for some tasks because of the garbage collector. But provided you AOT compule, disable the garbage collector and do manual memory management, it should.