
Derek V. answered 03/27/19
College professor for Philosophy and Logic!
Some theists have suggested that a reason why God would want to create is that God is love, and as such, God wants to share him/her self with another being. Other theists (e.g. Aquinas) would disagree and say that God, in virtue of being God, is perfect and whole in himself/herself. Since one only wants what one doesn't have but thinks that one needs, and since God has everything he/she could need, God could not want anything, and therefore God could not want to create. A better question for such theists would simply be: "Why is there anything other than God?"
Also, just a comment on your set up: Though there are some theisms which are inconsistent with evolutionary theory as most would understand it, this isn't true for all theisms. That is, there is at least one theism according to which God creates matter and perhaps the first living organism, and natural selection takes over from there. For this sort of theism, the creation vs. evolution dichotomy is a false dichotomy.

Robert B.
02/25/23