Amount of software running on .Net Framework is mind boggling. If there is not 100% compatibility with .Net Framework on Windows running on Linux, forget it. I know of a company still using Visual FoxPro in 2020 and it was still being maintained.
Just like COBOL, across insane amount of businesses/enterprises/government, there are hordes of Windows machines, using technology that last saw updates in early 2000 computing away. Their last supported Windows Server was probably 2008 but somehow they still run on Windows Server 2019 and those licenses are not cheap.
Sure, Windows Desktop is clearly becoming "Whatever" by Microsoft but it's also pretty cheap. NT Kernel and UI work has to be done for server side and until that cash cow is dead, shoving slop into Windows Desktop is cheap revenue stream on work they have to do anyways.