Also, there seems to be a lot of confusion about this: JHONEN DOES NOT AND NEVER HATED INVADER ZIM.
Seriously. He doesn't. He hated arguing with Nickelodeon about insignificant issues, but he doesn't hate the show. He's very proud of it. He continues to talk to fans about it. Also, if he hated it so much, he would have refused to do the DVD commentaries.
Jhonen Vasquez is actually not the cold-hearted hateful person that everyone seems to want to think he is. Yes, he makes disturbing comics, but he's actually a pretty nice guy. I've talked to him a few times, and despite me being an overly obsessed fanboy, he put up with me pretty well. And in interviews and con appearances, he's very nice when answering questions.
But yes, the main reason for the cancellation was the overblown CGI budget. Though they probably could resurrect the show now and it'd be such a huge hit that it wouldn't matter anymore. It was ahead of its time. However, they seem to want to bury the show yet still sell merchandise. They'll never admit that canceling it was a mistake.