It's usually the people who stay low-key and move like they don't even know that they're famous. One of the easiest ways for celebrities to fall off are those who buy into their image and get involved in things they shouldn't be a part of.
From my understanding, it's easier to handle fame when you're not that visible to the public. Matt Groening created The Simpsons and there's about a 50/50 chance you know what he looks like, and he's rarely in the news for anything unless it's Simpsons-related. Meanwhile, there are many people who contributed to The Simpsons over the years and had more of an influence on what the show became than Groening did, but most people (outside of hardcore fans) don't even know their names.
There are people who still believe Seth MacFarlane does everything on Family Guy because he'll always be the first person you associate with the show, but he hasn't done any writing for it in almost ten years.
