Futurama was a different type of humour than Family guy and the simpsons for that matter. Some people got, some people didn't.
Family guy was great, but you have to admit, a lot of the jokes are pretty well, rudimentary... and thats what makes the show so perfect.
what killed Futurama was it's time slot. I still don't understand why fox insists on having comedy shows during the 1900 Sunday timeslot as they ALWAYS get preempted by the NFL.
As for the Simpsons, Matt Groening, he has become a figurehead of sorts, as far I as understand he only goes into the office once a month and looks over some stuff, perhaps give an idea or two. The guy who runs the show now is Al Jean, who was one of the first exec producers on the show - he and Mike Riess later came up with the Critic, another show that died a premature death.