So, Zeus can’t work Demeter over. He simply has no way to leverage her. She has all the power when it comes to crops, so Zeus has no choice but to work on hades. But the thing is he’s also stonewalled as he doesn’t “want to offend Hades.”
But why? Well, like Demeter, Hades has his own domain, though his is more literal. Hades, Zeus, and Poseidon all divvyed up the world by drawing lots—and Zeus rigged the game so he would get the sky. But just because Hades got the fuzzy end of that lollipop doesn’t mean he’s powerless. In fact, Hades wields an incredible amount of power. Hades alone determines who goes where in the underworld, or, more specifically, who is even allowed in. that’s his leverage against Zeus.
Hades could decide to do as Demeter does and exercise his control over his domain. In this case, he could refuse anyone entrance to the underworld. If this were to happen, people on earth would never die. They should die, they would want to die, but they would be refused entry.
So on one side, Demeter is threatening to starve humanity out. On the other, Hades would refuse them entry into his realm. It’s a clear stalemate. Well, almost. Zeus is the clear loser.