This is why I use the KJV it explains the three heavens. They were created in order.
The heaven where God was going to move to.
The firmament of heaven where the celestial bodies are.
The open firmament of heaven where the birds fly.
Good golly this is repetitive. The physical world is not the question. Why create heaven? I'd be just as happy in an eternal retirement home where He was before the beginning.
Totally off topic but I'll try and veer it in the right direction. The answer is of course not so why create heaven when God could have just stayed there, created the world and the universe. Why did He need a heaven? A vacation home?
Um, according to the text and the gist of the op the formless and void was after the period I'm asking about.
Why did God need to create heaven? What was wrong with where He was before He created heaven and earth, and the darkness and the formless and void?
In the KJV that's not the case. The firmament of heaven was created afterward to separate the heaven of 1:1 from the earth. The celestial bodies are there.