*longs your snoot*

their big eggs are actually that size for a similar reason to human babies having massive heads!! being bigger at birth can be important.

kiwi are trying SO HARD to become mammals. fur-like feathers, whisker-like feathers, little beady eyes, nocturnal, great sense of smell.... that's basically a mammal!! they're well suited for life on the forest floor.

their big eggs work alongside these adaptations to give them a leg up in the bird world. their young hatch already feathered! they're precocial, which means they're born with the ability to open their eyes and move around. like foals.

big egg = more powerful offspring from the get-go. babies don't need to spend precious time vulnerable while they develop on the ground when they've already done all that in the egg!