I think nostalgia has something to do with it. Kid's cartoons used to be smart, funny, with jokes you wouldn't get until you were older. Now, it's all just stupid humor and lousy stories.
Not that all cartoons now are like that, mind you, shows like Phineas and Ferb, Avatar: The Last Airbender/Legend of Korra, Young Justice, The Amazing Spiderman, and Avengers: Earth's Mightiest Heroes are all really good, so why can't they ditch the crappy cartoons and bring back the good ones? And why does Toonami have to be part of Adult Swim?!
*SIGH* I freakin' hate TV stations...