Also, even if there was a deeper cause contributing to both ("causing it" is much more rare than a common contributing factor) you could cure one bot not the ot

Also, even if there was a deeper cause contributing to both ("causing it" is much more rare than a common contributing factor) you could cure one bot not the other if you don't address (or don't even know) that common factor but use some other path to address one problem even without knowing the full picture. When (as is common) there are many contributing factors solving one problem may be done by addressing only one or some of them, and that may not be the one that also contributes to some other (visible) problem. So "curing one also cures the other" would only work in an incredibly specific scenario, while there are many others possible that allow some sort of common factor somewhere, among many others.