>Then he would start treating the addiction personality and causes, but in many cases the patients would just stop coming and live three or more hours of every day in the gym.

one can speculate why addiction hasn't been selected out - may be because it probably provides significant advantage when channeled right. Some achievements/mastery/etc. require tremendous focus and huge amount of persistent work which probably may be not doable on rational motivation alone, without the primal dopamine [over]drive.