>>714176667 (OP)Fujibayashi is to blame for this. Skyward Sword is also a worse game than Wind Waker, but it took even longer to make than Twilight Princess did, and somehow he still wrote the entire plot in an afternoon.
He also said the Depth in TotK were just auto-generated terrain by making an algorithm that inverses the overworld map with unique tiles, and that it "only took a couple of hours to generate."
So there's a tendency with this Zelda director to take minimum 5 years and a lot of that time is spent faffing about.