More topical references would help if there was a strong commentary aspect to Futurama, but it's never been that kind of show.
The simplest explanation is jokes are the bread and butter of a comedy and they just aren't that great in Hulurama. Having rewatched it recently, Foxurama also leaned heavily on the plot of individual episodes, but so far the plots feel like retreads or just not particularly interesting.
Which now that I think about it, all of this can be said about The Simpsons.