While I get your point, I personally prefer it this way. Whatever Microsoft will put out will at least be “ok”, regularly bug fixed and supported for ever and ever.
I prefer to having an ok default and just rolling with it.
But this is a tacit agreement in the .NET world. It's not only about libraries written by Microsoft. When sensible libraries such as Automapper or Newtonsoft JSON appear, everybody defaults to them.
A big thing that people often don't understand about .NET is it has the perspective of being all things to all people.
One example of this is that it gives first class support for supporting living extensible systems for long durations like decades which is often not really the case for other stacks. Hence the prevalence for approved long term supported libraries typically with first party backing from MS.
Another aspect of this all things to all people is that it has lower level closer to the metal performance features that people only used to high level stacks often mention they don't see the need for (although they don't say it like that!).
Another aspect is you can do pretty much any kind of application in it, from web to native to high performance games or latency sensitive systems (with some special techniques) to well almost anything. The ability to access low level performance while still having high level general ergonomic APIs is critical to this.
In the .Net world, if MS released a certain library, that would become the de facto choice for nearly everyone in the ecosystem. Competing with the MS options was almost impossible.
So even if the MS choice had a lot of flaws, it would remain predominant.
Which meant that as long as the MS option was good enough, you wouldn’t see too many alternatives unless they were an order of magnitude better.
And a large reason for this was the closed source nature of .NET.
In the open source world, even if the primary vendor option is great, but it has only a single minor issue, someone will invariably fork it and fix the minor issue. Which puts competitive pressure on the primary vendor to incorporate that fox, or if they’re unable to, see a lot of people migrate to the competing, slightly better offering, which is easy to do since it’s basically the same product with that 1 slightly better fix.
In practice the original vendor almost certainly incorporates the Fox, especially since it’s so easy to do as someone else has already written the code for it.
So IMO the problem with the .NET/C# ecosystem used to be it’s closed source nature, which led to very little competitive pressure for improving tools and libraries, unlike all the primarily open source alternatives you mention.