The idea is to tell the user that the key exists, just not enabled right
now, and why.
Maybe it should be used only in some places, and not others. For example,
Boxes should probably unregister and not disable as to allow other boxes to
take the key. In that case no disable explanation will help.
Maybe disable should still steal the key but not use it. Where disabling is
used to make keys behave consistently and not depend too much on mode,
while also have the reason a key is not working shown somewhere.