In terms of speculating why Man O' War ducked the Kentucky Derby even though he would have been a heavy favorite ... his owner certainly wasn't the most sporting man to say the least and he later ducked other tough spots that season where he could have faced good older competition.
However, his erratic temper may have also had something to do with it.
Man O' War's owner did campaign War Admiral in a far more sporting way. War Admiral did ship for the Kentucky Derby -- and he did eventually bring him back at age 4 where he faced Seabiscuit in a famous match race.