Forrest actually seems to be a fairly honorable man by the standards of the Terran Federation. Presumably this led to his career prospects not being as good in the mirror universe, and also had a knock-on effect with Archer's career.Sheer ambition on the part of evil mirror-Forrest, I would guess Because it was a mirror universe. That's a stupid question.y7Because Forrest clearly wasn't very good at anything in the Mirror Universe, so he was stuck as Captain, which held Archer back from becoming Captain.Mirror Archer seemed to be unluckier than his Prime Universe counterpart. His makes numerous references to making a contribution and Hoshi seems amused when she read about Prime Henry Archer's. Most importantly, Hoshi says Archer was the subject of a Command conspiracy to deprieve him of Command. In the Prime Universe Forrest was responsible for the pick, Mirror Forrest probably picked himself.Honestly--because the writers wrote it that way. Forrest was killed off earlier in the season, and the producers probably wanted the actor to get another paycheck.