This list to me reflects a different element of the .NET ecosystem: .NET teams don't just buy into .NET, they also adopt often buy whole hog into a grab bag of other MS solutions alongside.

Are Windows Server, SQL Server, Azure DevOps, Teams, Chocolatey, and PowerGrep really a better dev experience than Linux, Postgres, Github, Slack, apt, and actual grep?

Many are debatable, but SQL Server & Windows Server are honestly a huge pain to deal with, and on top of that cost a boatload in licensing fees. Even Microsoft has decided Azure devops is a waste of time post github acquisition and it is apparently eventually going away. Teams honestly sucks in comparison to Slack.

That is seriously outdated in 2021. A modern .NET developer use Postgre, SPAs like everyone else, vscode notebooks, VS Code, etc.

Visual Studio or JetBrains rider is the only thing a professional developer needs. Which is tiny investment for a professional. The rest of the products I have not seen in new projects use for years.

Why is any of this necessary?

It's not, although Microsoft absolutely tries to make it much easier to write/deploy/maintain C# in an all-Azure tech stack. That's good or bad, depending on whether you have other reasons to be on Azure.

I'd say Visual Studio (not VSCode) is pretty much the only not-really-optional, not-really-free dependency. I suppose that means you also need to buy Windows.

Personally, while I use(d) C# for work and I think it comes with a solid toolchain and I have no big complaints, I have never chosen it when I could choose the stack from the beginning.

With lsp-mode you can write C# in emacs and still get Intellisense code completion!