Becasue it is a place where you are not only told it is ok to revert back to your unstressful/ no resposibilities childhood, it is ENCOURAGED and almost required! You are in a bubble environment 24/7 of play and fun and constant entertainment, blocking out every possible obligation or unpleasant issue you have to deal with daily in the "real world".
Thank heavens we have such a place to go to if we choose. I am a WDW addict, believe me....and to me being able to choose a place to go where most peers are in the same frame of mind, theraputic.