The BBC - and indeed any broadcaster - is aware of the need to refresh formats, and every presenter has a definite 'shelf life'.
It may be that Mr Inverdale is seen as less that acceptable after his unfortunate word slip, and his inappropriate remarks about a lady player's physical appearance.
Ms Balding has proven abilities as a broadcaster, and is very popular.
No, she is not a 'star', or indeed a 'national treasure', but I see no indication that anyone infers that she is either, or both.
As for 'political correctness', I think you are miles off the mark there AOG - Ms. Balding works because of her presenting skills, not her orientation which neither she nor her employers make any reference to at any time - nor indeed should they, it is irrelevent.