Q. Re: “Why doesn’t God save everyone.” I agree with your answer up to a point; but it avoids the real question. (In my mind; at least.) Here it is: God; in His foreknowledge; knew who would open their hearts to Him. However; He also knew who would not be receptive to Him. He knows who will be eternally lost. Why create a person who will suffer eternally? Would it not be better (and…I say this with reverence) be more loving not to create those people?
A. Knowing the future is not the same as controlling it. God has always known who would choose to be saved, but intervening in the procreation process to allow only those who will choose Him to be born would violate our agency (our right to choose). Remember, although He’s a loving God, He’s also a just God. He loves us enough to have given us that right, and His justice requires that we be allowed exercise it without restriction.
Remember, we were all destined for Hell because of our sins. But God so loved the world (everyone) that He gave His one and only Son, that whoever believes in Him shall not perish but have eternal life (John 3:16). Anyone can choose to alter their destiny from death to life, but it’s a choice only we can make.