The Simpsons have changed and evolved during their decades-long existence. During the earlier seasons they were a lot more about emotions, then other writing teams came and opted more for a surreal series of gags, then others for the metalinguistic humour and parody.
Interestingly, this season had a special episode that Judd Apatow wrote when he was a young, struggling nobody, “Bart’s New Friend” and you can see how it stands out, not because it’s particularly better, but because it goes for a sentimentaly in the relationship between Bart and Homer that contrasts with the current, more cynical style.
But different doesn’t mean worse. The Simpsons has always had top notch talent, even in their biggest slumps.
Why? It’s pretty safe to say they’re still making money off it (and besides the show proper, it’s a whole franchise that has sold plenty of merchandise, toys, video games, a feature film, etc.). From a business perspective, if something is profitable, you don’t put a stop to it. Especially not because Some Guy From the Internet thinks it “should”.
It’s not a question of how talented the writing staff is; blaming them just obscures the issue. There’s only so many times you can visit the same well before it dries up. How many times can you watch Homer catastrophically screw up, apologize and be forgiven? How many wacky “Homer’s new job” episodes can you watch without being reminded of half a dozen better variations on the same theme? How many “Wow, [Celebrity Name]!” cameos does one show need? That was really why I stopped watching: it became the same thing over and over, and less funny each time.