When extending C++ editor, Comment Selection command is not available

[fdarvea]

Description

I extended the C++ editor in my own editor using a MEF component.

[Export]
[Name("mycpp")]
[BaseDefinition("C/C++")]

When a open a file, the C++ comments are green as expected.
However, the commands Comment Selection/Uncomment Selection are grayed out in toolbar and missing from Edit-Advanced menu.

With the keyboard shortcut, the message is
The key combination (Ctrl+K, Ctrl+C) is bound to command (Comment Selection) which is not currently available.

How can I make the commands available?