I admit my experience is mostly with JS deployed on Linux, but ASP.NET seems like a good framework with awesome tooling. Also using the same language on the frontend and backend is very useful and I consider C# the best option for Windows frontend work.
Not that I'm saying NodeJS backend with Website/Electron frontend is bad, but ASP.NET backend with WPF frontend seems great as well, just with more enterprise-oriented trade-offs, support cycles longer than one year but no cross-platform support (yes, ASP.NET core is a thing now, but that's a very recent development).
And compared to the cost of engineers I don't think many companies are that worried about spending 50% more on infrastructure.
Legacy ASP.NET web pages might be harder to migrate, however, newer web sites can also be implemented using ASP.NET Core MVC. It seems other departments in Microsoft do understand that their code base needs to be able to run on a Linux OS, otherwise they are at risk of losing market share. Even SQL Server can run on Linux now.
Not that I'm saying NodeJS backend with Website/Electron frontend is bad, but ASP.NET backend with WPF frontend seems great as well, just with more enterprise-oriented trade-offs, support cycles longer than one year but no cross-platform support (yes, ASP.NET core is a thing now, but that's a very recent development).
And compared to the cost of engineers I don't think many companies are that worried about spending 50% more on infrastructure.