People want to fix blame whenever something goes wrong. There are several reasons for this, including (but not limited to):
1) You need a person to blame in order to file lawsuits.
2) It makes people feel better if they can find someone to blame (other than themselves) for what happened.
3) If it is a political thingy, you can get some serious political points if you can find a way to blame the people you compete against.
As far as building on experience, that is exactly what they are doing now, regarding Katrina. Hell, there is a person on this board who was responsible for finding things that went wrong so that it can be improved in the future.