Hey, no need to dive so deep into Demeter's story. My actual question was about Zeus if you actually read it. Like, why did he let Demeter's whole 'withholding food from humans' thing slide? We've seen Zeus punish other gods for way less. Hera, Prometheus, and Hephaestus come to mind. So, what's the deal? Why not just assign agriculture to someone else? The gods' roles aren't set in stone. They're basically rassigned, like when the three brothers drew lots to determine who'll rule over what. And you'd think Zeus, being the literal all-wise and all-knowing king, would avoid setting up a situation where one god beneath him (any god, not just Demeter) could wipe out humanity.
Ignoring the fact that, no, it wasn't at all clear that the ask was about Zeus, let's get into this.
Zeus punishes the other gods when they challenge his authority or violate the customs associated with his honors.
Hera tried to dethrone him—a direct challenge to his kingship—, so he hanged her from Olympos in chains.
Prometheus stole from Zeus's house—a violation of xenia—, so he chained him to a mountain and sent a bird after his innards.
I'm not even going to touch on Hephaistos because the version of the myth where he throws him off Olympos for interrupting a domestic dispute between him and Hera comes from the Iliad, and interactions within the pantheon in the Iliad are very obviously meant to be comedic (at least it's obvious to me).
If Demeter wants to withhold her gifts, then that is completely within her rights as a goddess of agriculture. She is not violating his honors or challenging his rule by inhibiting agricultural processes because agriculture is hers. Zeus can't punish her for operating utterly within her sphere of influence.
There's also the fact that, whether we understand his process or not, Zeus is always playing 5D chess while the rest of us are playing checkers.
In other words, he is always 1000 steps ahead.
By setting up the events that would lead to the blight, he ensured the creation of the seasons and the Mysteries, which guaranteed humans a better life after death.
Another way of thinking about it is that momentary chaos begets better order.
Also, as an aside: You are seriously misunderstanding the point of the lot-pulling myth if you think it indicates that Zeus can re-apportion honors and spheres of influence as he pleases... The myth is meant to show that Zeus's kingship was a matter of fate, not that he can reorganize the pantheon all willy-nilly.