Alternative explanation..
Maybe the key didn't actually leak at Microsoft and it has just been told to take the hit.
Maybe what really happened was that the key was stolen from one of the many agencies it must be sharing the key with, but they can't afford the embarrassment. We're as used to Microsoft causing security problems as we are to Trump committing crimes or Musk overpromising that it would not really register much..
After all, this is the same government that told you your luggage was still safe despite their mandated backdoor*, and you can get TSA keys now even from Amazon..
* If this sounds familiar, you're thinking of the insane idea to demand a backdoor into encryption that somehow seems to appear every 7 years or so, but in British politics.