The show’s decline can be attributed partly to its own past; what was once a target of satire has now become part of mainstream culture. Another factor is the current style of comedy that relies on finding humor in things themselves, rather than clever jokes. It feels like audiences are supposed to react with laughter simply because something is presented, as if being told, "Look, it's a refrigerator! Be amused!" This shift has changed how jokes are structured. Previously, celebrity appearances were the focus of ridicule; characters like Mulder and Scully were parodied by The Simpsons. Now, the joke seems to be the celebrity’s presence itself – simply pointing out “It’s Lady Gaga” or “Here's Michelle Obama.” There is no satire or parody involved; viewers are just expected to laugh at the fact that a famous person appears in the show. A further issue is the way jokes are now delivered, mimicking shows with laugh tracks. The Simpsons used to avoid this kind of setup, but now there’s almost an intentional pause built into the writing, as if anticipating audience laughter. Jokes were once layered on top of each other, creating a rapid-fire succession of gags within a scene. Now, it's more like: joke, pause for acknowledgment, then continue. Ultimately, people aren’t really laughing because the show no longer satirizes culture, doesn't spoof its celebrity guests, and has largely lost what made it distinctive.

Source on TMDB