It Set the Foundation for Modern Adult Animation
Pop culture frequently resembles an ouroboros, eating itself endlessly. Writers routinely include allusions and homages to the works that inspired them in their works, and movies and TV series frequently cross-reference one another. You would have a difficult time finding much in the field of comedy over the past 30 years, especially animated comedy, that hasn't been impacted in some manner by The Simpsons.
The Simpsons is often credited with inventing the genre of contemporary adult animation, according to Seth MacFarlane, the creator of Family Guy and American Dad. His programs, as well as other titans of animation like South Park, Beavis and Butthead, King of the Hill, Futurama, and Bob's Burgers, have all seen their success credited to the path established by The Simpsons. He considered the show "wholly original." And that's not to imply that the programs resembled The Simpsons in any way or, in the case of something like Rick and Morty, duplicated it. But it's arguable that The Simpsons' irreverence, wit, and heart laid the foundation for any of these other series to establish their own audience.
In essence, The Simpsons demonstrated that cartoons could exist that weren't just for kids for the first time since The Flintstones in the 1960s. It could deal with mature topics, even dark ones, in a way that would pique the interest and amuse an adult audience. That had not really existed prior to The Simpsons, and without them, it is uncertain whether any of the well-liked animated series of today would have ever been made.