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.
I would hardly say that TDD removes the need for an integrated debugger. Being able to inspect the state of a system the instant a test fails sounds mighty useful to me.
Also, software builds being driven by an external tool has been common since at least make(1), so it's hardly a ruby/node/python thing.
I've been the new guy on teams that did not use the ide for debugging (insanity in the Java world, right?) and was perceived to be a super star because of my ability to trouble shoot and drill straight down to root causes. Learn and use your tools people!
IDEs are fine, but when you remove the need for an integrated debugger in favor of TDD the need for an IDE diminishes.