You pay these people for their PhD level knowledge of math and stats, because that is a sparse skill: No matter how many Coursera courses one does, you can not

You pay these people for their PhD level knowledge of math and stats, because that is a sparse skill: No matter how many Coursera courses one does, you can not upskill anyone to that level (at least, I have never seen it). So, if their time is better spent applying that knowledge rather than thinking about infrastructure trivialities, then by all means, pay an engineer to clean up. In the end, that's still more cost-efficient. That being said, I refuse to believe that anyone leaving university today with a degree in stats/ML/econometrics etc. doesn't know git and can not be taught good programming that doesn't at least interfere with operations. But as soon as you start requiring your experts to do infrastructure, you are either wasting money, or you hired a quotation mark "data scientist" with a degree from medium.com and towardsdatascience.org or whatever - in which case by all means, require them to do engineering duties.