Why is the concept of juridical personhood, as against natural personhood, at odds with infinite duration? The law doesn’t place a mandatory span on the recogn

Why is the concept of juridical personhood, as against natural personhood, at odds with infinite duration? The law doesn’t place a mandatory span on the recognition of natural personhood anyway. If someone did live forever, there’s no law or legal obstacle to them doing so and exercising their rights in perpetuity.