Because Visual Studio Code isn't like Visual Studio at all. It doesn't support any of the VS extensions (because it's a completely different product).
Perhaps they shouldn't have given it virtually the same name then. I can understand that he had an expectation given the naming choice. It also means that this support is Windows only.
Because it's beta of totally new product which is Visual Studio only by name.
Nor should it be expected to
I expected it to. Oh well.
VS Code is more of a text editor and less of an IDE. I'd say it's target market is closer to Sublime Text's than Visual Studio's.
It would still make sense to add Rust support though.