I heard an interview he did on the radio. He was talking about old B-horror flicks like Creature from the Black Lagoon, and how when watching them as a kid he wanted to see the monster get the girl. That is what Shape of Water was essentially for, straight from the bull's mouth
Now, if monster movies are supposed to be allegorical about things we fear in ourselves, I suggest that del Toro might want to reconcile people with their own need for affection. The monster seizes the attractive woman, but is it to be threatening, or because he experiences the need for beauty in his own life?