The Simpsons have jumped the shark numerous times. Instead of having a plot, they jump from mindless joke to mindless joke.
They used to be a real family that happened to be cartoon characters. They had a real story line, did real things, et cetera. This is no longer the case.
Homer no longer has a job, has superhuman resistance to damage, is a moron. Lisa is your stereotypical liberal. Bart is an annoying ADHD boy.
Shall I go on, or is the point made?