I believe the main reason is because the US at some point will be called on to broker some sort of deal. To the extent we take sides the less effective we will be.
So, Bush is in a corner that he has to leave alone. On the one hand I believe and rational person would see his original words are correct but on the other as a potential judge in the roll of brokering a deal he must assume as nuetral a posture as possible.
And as I said before, for that to happen, Israel has to decide that it wants to survive more than it wants to be liberal and "reformist." There is a big question as to whether it will make the necessary choice.