That the kingdom has not been pre-fabricated by God Almighty is a disappointment to some in the kingdom, and gives them cause to question whether they wish to remain in the kingdom, and whether their work in the kingdom will be rewarded. They have two options.
Their first option is to work on behalf of the devil, doing everything he tells them to do, every day for the remainder of their lives, then receive the reward of death, because the devil's kingdom is designed for him and his demons, not for humans. The humans he uses are merely his slaves who assist him in building his kingdom. He may have made elaborate promises to them, but they receive from him no eternal reward whatsoever.
Their second option is to decide, freely and without compulsion, that they prefer to align themselves with Almighty God, choose the type of future they wish to have, and create that future using as their building materials only what God approves and provides. Their future belongs to them, the kingdom they build will belong to them, and they will have an eternity in which to live, work, and play in it. Their reward is eternal life, eternal joy, and eternal peace.
The Lord God Almighty El Shaddai