We know what causes the symptoms that are pfs. What we don't know is why some men are susceptible while others are not. This, imo, comes down to genetics. But as far as the symptoms, they are easily explained simply due to the effect of 5ar inhibition. Nothing to guess. Very straight forward.
Seeing as the end result of the enzymes actions are responsible for many different functions, it only stands to reason that everything "downstream" from this blocked or destroyed enzyme is going to suffer catastrophic failure which then leads to other system failures and errors.
But you are right in the fact that they simply can't make a pill to fix the myriad of damage done by inhibiting the enzyme.
At least we can do it, that's the only thing that matters.