>>149410932
He doesn't
Simpsons promotional artwork is done by Bill Morrison, who also worked on the comics. I assume contractually he has it so his name is put on there and Morrison and whoever are well aware and ok with it
I doubt most creators also do the promo art because of the sheer amount of art needed but I've heard at least Steve Hillenburg was involved with creation of some SB stock art, there's some scans of him giving feedback on artwork