>>712722543I think that's because Stan is just that much more anchored as a character. You know exactly what he believes in, and you can intuit his opinions on most matters in a way that you really can't with Peter or Cleveland, or Homer Simpson. Stan has that in common with Hank Hill. It makes for better, more focused writing. You can't really challenge Peter Griffin's beliefs, he could be in favor of something one episode, and totally against it in the next, and Cleveland is sort of a pushover. He can have preferences and try to advise others based on his morality, but there would never be a conflict of philosophy within him when something he considers foundational is put into question. He'd change his mind to accommodate others, or the apparent truth, readily.
Stan and Hank don't do that. They try to make the pieces fit, or impeach the flaw in what's challenging them. And sometimes they come away having made a point, and having learned something in the process.