Well i think is more of a cultural thing,
yesterday with some friends that work for Sony developing games for the playstation, were arguing about one of the nintendos top games, Smash Bros... they were mad saying playstation characters were as iconic as nintendo's... of course not... nintendo in popular culture way more symbolic that playstation characters even their consoles sell more...
culturally the union were more western iconic, they are present in mexican america war, civil war, indians wars... i remember playing indians vs cowboys and indians attacking the fort... Playmobil may not even needed the confederate soldiers... maybe was just a move to sell instead of indians, and stop the slaughter of union soldiers with cannons against the indians...
but again, the cliches in movies, the products we used, even our conception of so many things is based in icons that become symbolic... like santa, like valentines, like movies... etc...