At the same time Spiegelman was designing Weakies and Crust, he was also contributing to the counterculture by way of undergroundcomics that were decidedly for adults.
Del Toro was a good draftsman, but he knew that he would never be a master. (His favorite was Richard Corben, whose drawings, in magazines such as Heavy Metal, helped define undergroundcomics: big fangs, bigger breasts.) So del Toro turned to film.