It's been 3 years but better late than never.
Zeus wisdom was always present either within his judgement or by Athena's voice.
We should remember that Metis is the expression of something people had in mind at that time. As always myths are made by people and myths many times represent ideas people of that time had. Metis personifies a set of skills.
J.P Vernant, a French Scientist did a huge research on Metis. Maybe reading his book might enlighten you, because Metis as an entity is wrongly taken as just the godess of wisdom. Wisdom as a term is wrong.
Metis is a way of thinking. A way of thinking including trickster, wisdom, skill, engineering and many many other skills that come up to efficient problem solving.
Zeus efficiently cheating Hera alone, proves Metis presence. Nobody said that Zeus uses Metis wisely but nobody can say the opposite either. Who can defy his choices? His actions brought Hermes, Dionysus, Artemis and Apollo to the Pantheon. Not to mention Herakles.
It was probably part of what other religions say "part of a divine plan".
I admit that it is a good question though.