By going to VS Code they're jettisoning themselves from the .sln (solution file), .csproj (C# project file), MS Build world.
Project management and build files are being pushed into external utilities. This is kind of the way a lot of the rest the world (ruby/node/python) is going.
IDEs are fine, but when you remove the need for an integrated debugger in favor of TDD the need for an IDE diminishes.