There was no paper and pencil "in the beginning." So God had to do everything in his (figurative) head. There was no way to see what it would turn out like, so he did a few steps at a time and stopped to see what it looked like. You know, like choosing the carpeted floor color and having to look at it before you decide what color walls and drapes to have. Should the carpet and drapes match exactly?
So I can imagine looking up from earth at the vast nothingness and trying to decide how to fill that sky and how to provide warmth for life and food for plants and whether to tie them all together or make them separate.
And it only got harder to decide as he created life. Sometimes, he put eyes all over a creature to see if he liked that, or made the front legs too short (t-rex) or morphed them into wings. Tough calls in each instance. You know, why couldn't birds have 4 or 6 legs along with wings?
Unlimited power doesn't mean you know what to do with it. Put a blank canvas in front of an artist and he will spend time staring at nothing, painting over what he painted, yadda yadda.