What is a reason a theory cannot become a law?

Wonderful question! All too often, science is viewed as "absolute," but its very purpose is to ALWAYS QUESTION and develop conclusions based on verifiable, repeatable facts.

While we acknowledge the value of consistent relationships, the most stable ones are still subject to scientific scrutiny and are not, therefore, considered "Laws" in the scientific community.

Everything is a theory, to use the language of the strict scientific method. We hypothesize how some things interact and try to design experiments that support (NOT 'prove') those conjectures or not. The more evidence that a theory has, the more trust we can place in it; however, that does not mean that we can ever say that it is the only possible interpretation!

After centuries of useful service, Newton's "Laws" of Motion are still relevant in the macroscopic world. However, we now know that quantum mechanics has superseded Newton's "Laws" of Motion, which are no longer the correct form for all motion. Quantum mechanics IS applicable at both the atomic and macroscopic levels; it is simply too laborious to apply in every situation.

Furthermore, we use the term "Law" to indicate a long-useful Theory, but it does not mean that it cannot be modified. We cannot even say that Quantum Mechanics is the "final" accurate description of the motions of the universe.

A theory cannot become a law because they serve different purposes in science. Laws describe observable phenomena, often in mathematical terms, while theories explain the underlying causes and mechanisms behind those phenomena.