There was one episode years ago where the kids had a school news program and they had this great idea, put in a lot of work, and then it was "have to do it again next week" and they bail.
Most shows get old after season 5-7 range and have to keep reaching to stay funny, entertaining, engaging, and relevant. Once you change a show you tend to see fans splinter with some liking different periods or styles. I doubt if we were still saying "Oh my god, they killed Kenny! You bastards!" anyone would still find it funny. I think the "member berries" storyline is in part Matt and Trey fighting the desire to just do what is comfortable and familiar to appease people.
I get the criticisms people have, some episodes through the years have really fallen flat. I don't think anyone wants another Towlie centric episode. Over all though I'd take South Park mentality over what I see in too many shows to just be formulaic and boring.
