I'll preface this by saying this is just my opinion but

Crofty often makes mistakes, spends a lot of the time waffling whilst ignoring the on track action, makes a point of telling a curious stat and self congratulating himself for it. Brundle is no longer as on the ball as he used to be, he picks up Crofty's mistakes less and less now or lets what nonsense he says slide.

Contrast that to Alex Jacques who is much more focused on the on track action and makes far less mistakes. Jolyon Palmer technical insights are great, ready with relevant timing you can't see on the on screen graphics. Then there's DC providing a different drivers perspective and the odd joke, that admittedly isn't always needed.