While they might not do it regularly, they probably watch episodes of the show when it comes to television, making them reminisce about their younger days.
If an animated show has been running for more than two decades, it only does so if it is immensely popular and well-received by one generation of audiences after another, because, in twenty years, the viewers of an animated show certainly change, with new generations of children discovering, but, when it comes to SpongeBob SquarePants from Nickelodeon, we are positive that many teens and adults are watching it.