Kennedy had a lot of history with both Reagan and Ed Meese. Everyone expected him to be a reliable conservative vote. Unfortunately he has drifted left through the years. At the moment he is still the third or fourth most conservative member of the court. As we like to say in Sacramento, at least he's not Souter.
In other words he was another "in house appointee" like Miers. If Reagan could get it wrong, why are we supposed to just assume without question that Bush has it right?