What unusual distinction do all of these people share?

What common bond unites all of these people?

Steve Allen, James Brown, Johnny Carson, Bob Denver, John Entwistle, Stephen Jay Gould, George Harrison, Bob Hope, Linda McCartney, George Plimpton, Tito Puente, Joey Ramone, Johnny Ramone, Johnny Unitas, Barry White

(I won’t claim this list is comprehensive, but this definitely includes most of the available candidates.)

And guess where I cross-posted it?

7/7: Edited to add a couple of names.

All of them guest starred on The Simpsons as themselves, and are now dead. Anyone want to argue for a curse?