It would have made every bit of sense for highmountain tauren to be Alliance and would have been way more interesting. The Highmountain have no history with the Bloodhoof tribe, but do have a history of working with the night elves. It would have also left the Broken Isles a lot more evenly split with each faction taking control of 1 of the 2 major cities on the archepelego.
But no, daddy Blizzard couldn’t have it’s pet faction not getting all the best toys, so they gave the Horde both the races with all the lore behind them and pulled two random ‘races’ out of their butts to stick on the Alliance and call it a day.
That’s why the Alliance can’t have good Allied races.