Since he wanted the will of the world to help him manage his farm, he didn't consider using up the essence in the world heart to grant the potential to cultivate to as many creatures as possible. Instead, he immediately decided to foot the bill and leave the essence of the world heart completely intact.
Now that the world heart has gained access to infinite energy, it will be able to grow stronger much faster than expected. And with him giving the will of the world directions, it won't go astray or do anything wasteful.
Since his lifespan was limited, he picked the biggest creatures to invest in. All in all, he picked one thousand large animals and spent a thousand years of his lifespan helping them cultivate.
