Because we don't know why. We have many suspects, but no concrete evidence for any of those, and in many cases, not even clear mitigations. (Let's pretend for a moment it's e.g. all about PFAS, what do you actually do about them? And what do you do once there's the inevitable political outcry that it's just spoilsports from the other side trying to ruin your life?)

And so we medicate, because that's the only thing where people can say "my neighbor did it, and look, it worked for them, I'll do it too".