The devs mostly put palette swap versions of already playable races or poor replacements of races that players wanted to be playable for a long time such as High Elves, Broken or Ogres as allied races.
While I wasn't against the Dark Iron Dwarves and Zandalari Trolls, I feel like Broken, Ogres, Arakkoas, Hozens, Jinyus or Vrykuls would have been better choices for allied races.