From a fan perspective, I think it's because the Red Sox fans are used to having good teams, so they don't feel any special gratitude towards Dombrowski. They saw that he gutted their farm system in order to win now and then he is somehow connected to the Red Sox letting their star players go even though it happened after he left. For Tigers fans, the Dombrowski years were the only time they really had a winning team in the last four decades.