Well, I'm not taking a position on this particular DWI stop and all that is alleged. It's a one sided story at this point, and no video tape.
I will however comment on the "how dumb" question, which is a legit question.
In general humans are very dumb and numb as to learning from experiences. Yes there are some singleton events which people do learn from, they are not rare, but as a class it is difficult to say what common characteristic such events share.
In general folks need to be taught to learn from experiences, and teachable events need to be reinforced as "this is something we learn from".
Actually if you dig around in the thread, there is video available of a couple of the events.