Why do authors STILL write...cliches?

It really surprises me to buy or borrow a new book to read FILLED with cliches and stereotypes. Examples would be that the popular girl is usually blonde and dumb, or we'd have the stereotyped smart Asian kid when we know it's not always true. And as for cliches, we have in fantasy books the loser kid who's a nobody who all of a sudden is on a mission to save the freakin world and they all of a sudden can fight like a ninja when at school they get beat up by stereotypical bullies. There's so much more but I don't want to make this question too long. I swear, stories these days are practically a phone book of cliches! Why, why, WHY do these terrible, overdone plots manage to get published?