Jokes aside, your statement is only true under the assumption that the original idea is cheap and trivial, which is not true for a large number of patents. For hardware patents such as the ones filed by Tesla that helped significantly advance modern technology, they are often non-trivial, yet he was never wealthy enough to produce his inventions at scale and relied heavily on corporate partners to do so. If he was not able to own his patents without actually produce the products himself, this arrangement would never have worked.