Great point mentioned in Reddit:
Honestly I'm wondering why they'd announce it at all.
Why the need to announce it worldwide now and fast?
I think it very plausible that he is facing health issues, possibly something terminal. Not at all unusual for a person of his age.
Well he would not be removed though, all other ill GB members stay on til death even if they do no duties, they can still be on the GB and have their experience. Whilst he may have health issues I can't see that being the reason for no longer being on the GB nor the very small formal announcement without the words around his service.