"IMHO" most hermies are results of poor genetic selection during breeding. Either from stressed plants that were genetically inclined to begin with, or accidental pollination by a stray hermie flower. MJ is known to produce a male flower or two, late in the flowering cycle, as a last ditch effort to reproduce.
That in itself, is not neccessarily a genetic fault. But, what usually happens, is some one then uses the few seeds produced by that pollination to grow. Resulting in further promoting the herm' trait.
Possiibly under 'ideal' environmental conditions, those won't hermie. BUT the hermie trait is there, lieing just below the surface waiting to rear it's ugly head. Future generations are sure to exhibit the trait.