Much of the science of bio-mechanics was abandoned and thus the Mech's have had little information on how to create or repair themselves, though they have learned over the last century through trial-and-error, sometimes with monsterous results. Because the Mech's cannot reproduce, they often bolster their numbers by abducting wounded soldiers of their enemies.
Though most Mech's are still in servitude of the humans, sometimes used on space vessels in operations that would have ill-effects on a normal human, some Mech's have escaped their bondage and are now raalying to free others of their kind.