The issue I have with the "new Simpsons"...which is now like 10 years of Simpsons...is the fact that they don't focus on a meaningful show. Just a quick lame setup and punchline. Setup and punchline. There is no substance to the show.
There are no longer interesting situations. It almost seems as if the original episodes had a particular situation, and the hilarity came in seeing how the characters reacted. Now the episodes are "Lisa does something", "Marge does something", "Homer does something", etc.
Futurama remained consistently great because the characters are put into interesting situations and it's funny to see how they react and behave. Each episode has a storyline and there are elements of suspense, drama, and action.
When was the last time there was a moment of meaningful suspense in The Simpsons?
Again, the problem with The Simpsons can be summed up by 2 words, "No Substance".