Because people speak in rough drafts, as they also write in rough drafts.
If Clive Bundy were to sit down and write out his thoughts, and then go back to them a few days later and edit them, and then take a third look a week later, he would likely do better expressing what is on his mind.
As would most of us.
But he didn't. Nobody held a gun to his head and forced him to hold his presser and say what was on his mind. So he has nobody to blame but himself.