Quote Originally Posted by kingerman View Post
Because we sleep right through them and aren't normally trying to remember anything.You wake up and suddenly the brain is flooded with input, quickly crowding out what was only in short term memory (your dream).
Pretty much a perfect explination.

Most people don't pay attention to there dreams so they don't remember them. And by the time 14+ your dream recall is so down the toilet it takes work to get it back up.