Can you install it [edit: the .Net 7/8 platform that sounds interesting, not the IDE] for free on a Linux server and get the same benefits? (This isn't advocacy, it's a literal question about something I don't know.)
Monetizing software is so incredibly indirect. Obviously companies don't make any money on free frameworks and tooling. These days, using C#/.NET maybe/kinda/sorta increases the chances that you might deploy on Azure or use Azure services. That tiny (or not so tiny) uptick easily funds all C# / .NET ecosystem development.
I'm not sure why they do not open source the debugger. I suppose it is obvious to some extent that some companies (JetBrains) are able to charge for high quality tooling. Microsoft makes a trickle of money from Visual Studio professional.
Though the objective function and decision variables are somewhat opaque, this is clearly an optimization problem.
The why is Visual Studio. The VPs running that div are a bunch of Muppets who are constantly trying their best to destroy the OSS .Net projects reputation.
The cynic in me suspects all the drama was directly related to Scott Hanselman suddenly losing interest in bloggin.
I prefer Rider as a C# IDE whether it's Windows or Linux, although the last time I was doing this there were still a handful of things you needed VS for.
https://learn.microsoft.com/en-us/dotnet/core/install/linux
Also VS Code, an open source IDE with first class support for .NET languages:
https://code.visualstudio.com/docs/setup/linux