The "dumb is funny" approach has been around forever. In this century it seems particularly that southern (US) comedians went this route and no other. Minnie Pearl, Stringbean Ackerman, on to the Hee Haw TV show. The most interesting were Homer and Jethro, who didn't start out to be comedians at all, but they found more of a market for that than for string jazz. They were also very good at it, but the subtleties of some of their stuff was, I think, lost on much of their audience.
The thing that bothers me is the effect that Southern-based sitcoms, starting with the Beverly Hillbillies and reaching a peak with the Dukes of Hazard, had on regular people in this part of the country. The Foxfire series of books from north Georgia were started by a public school teacher there who noticed that his students were taking the TV version of their own culture to heart, rather than learning about it from their family and neighbors. He sent them out to interview moonshiners, farmers, and all manner of local mountain folks so that they would get a real picture of their own culture. But, the phenomenon did not go away. A longtime mayor of my small hometown patterned himself exactly after a Dukes character (the mayor). He dressed like him, talked like him - it was damned embarrassing. Even members of my own family started saying things like "you is", "we'uns is goin to town", etc. I hate it but what can you do?
So, yes, particularly for us in this part of America who do not participate, this dumb character act that gets humorous attention is not very funny anymore; again, it's damned embarrassing. It becomes a theme in national media every time a big thing happens here (like when Carter, and then Clinton were elected president), there were pages in Time and Newsweek about "how to talk southern" and so forth. We are not all idiots here; indeed, if I may say, we have produced most of the American art forms that the rest of the world knows anything about. But the popular vote is clear, even in regional and local media: Most of us seem to like it when other people think we're stupid. Maybe one day this plague will end.