How to answer "why are you leaving your current job" with specific scenario

ETA thanks to you all for the suggestions! I didn't expect so many replies in such a short time. To clarify a bit for those who might not have read my replies, he is in a trade (let's call it "basket weaving"). He was hired to be a basket weaver, but most of his current job involves making cardboard boxes. He's not happy with the job because he's excellent at basket weaving and enjoys making a variety of very intricate designs based on custom orders. He would actually be weaving at the other place. I think I will suggest he say "I absolutely love weaving baskets. X hired me as a basket weaver, but a majority of the tasks they have assigned are in other unrelated areas and I'm not fulfilled in the position." And then add some stuff about what he knows about their operations and how they align with his goals. I will definitely caution him not to say anything about the bad management and violations. I'm a manager and I think I would be put off by an applicant unloading that during an interview.

My spouse works for a company that is violating the FLSA regarding wages. There are other issues as well (OSHA violations, a new male supervisor allegedly using a mirror to look up into men's bathroom stalls to see if people are playing on their phones on company time - spouse hasn't experienced it directly so I can't say with certainty it is true). He's only been there for 2 months; previous job was 6.5 years and he's not a job hopper.

He has an interview tomorrow with a different company. If they ask why he is leaving, how should he answer the question? I think it would probably not be good to divulge that the company is violating laws, but I'm not great with being politically correct. Appreciate any advice you have!