Many transplanted seedlings do not grow because –

Root hairs are extremely delicate, thin-walled outgrowths of the root epidermis that are primarily responsible for the absorption of water and minerals from the soil. During the process of transplantation, these fragile root hairs are often broken or lost. Without a sufficient number of root hairs, the seedling cannot absorb enough water to sustain itself in the new environment, which is why many transplanted seedlings fail to grow or survive.