I don't think it's that the FDA or pharma companies don't want you to think about, I think it's just very difficult to properly study the effect of things that take a lifetime to manifest.
Maybe moving to a city with better drinking water is the best move for a small subset of the population. There's no sinister cabal trying to hide this, there's just no incentive for anyone figure this out for you in an individual basis.
I could see pharma working the other way though. If you could identify a location with a population who exhibit a deficiency and your drug is more effective there, there's an incentive to better promote it there. I don't think the industry is sophisticated enough at this point to accurately track this though, as individual patient response is difficult to measure and report on.
Source: dated someone that did marketing for one if the top 5 pharmas.