This is similar to comics and webcomics. It turns out that if you have your own website, you don't have to satisfy the censors in order to post anything.
Sometimes editors have good reasons not to let cartoonists put anything they like in the funny pages or the political cartoons, but the end result is usually very sterile. There's a lot of things you can say in that medium (e.g. the work of Bill Watterson or Gary Larson), but also a lot of things you can't.
That's a problem especially for political cartoons, because they usually poke fun at specific people, but you can't poke fun at just anyone because readers might get mad. The idea that there's an Overton window for people it's socially acceptable to ridicule should make us at least a little bit uncomfortable. Sometimes it'll be the emperor with no clothes and that's fine, but we might want to include the guy that sold him an invisible robe (but they own the newspaper too), and to exclude the kid who told everyone the emperor wasn't decently attired.
And now anyone can be a cartoonist.