To have fruit. That we might bear fruit. That's the exact reason. We fail when we don't have fruit to meet the divine expectations of the farmer, who is God. Fruit only appears when the when the seed is welcomed and nourished and acted on and allowed to develop.
Fruit comes from a right relationship between the seed, sunshine, water, and good soil.
Jesus says that fruitfulness is proof positive of the new life. That's how we are known. The true Christian will constantly be producing fruit. And so Jesus' parable is talking about being fruitful. The seed wants to grow in our life.