"why would God use means to bring that about?"
Because we are not robots.
It is because of God's great love for us that we are saved.
God desires us to pray and spend time with God in worship, He wants to communicate, interact, show favor, love, cant do that with a machine.
It is God's good pleasure to give His kingdom to those He has chosen to know God.
4 But God, who is rich in mercy, because of His great love with which He loved us, 5 even when we were dead in trespasses, made us alive together with Christ (by grace you have been saved)
All of this has a lot more meaning to a Calvinist because it shows God made us alive who were dead in trespasses and to be dead means to a Calvinist to be like putrifyingly truly dead. A lot of people don't think they are dead now and a lot of believers did not think much about how dead they were before they were saved.