Aasimar, Soul Knife, and Psy Warrior have all been through rounds of UA before and published in previous books - their popularity is established. The question is "Do these options have support?", and they already know the answer is "Yes", so the need for additional playtest feedback is negligible.
By contrast, replacing "half-elves" and "half-orcs" with a "one-size-fits-all" system that removes mixed ancestry from the mechanics of the game system and turns it strictly into a roleplaying choice doesn't need feedback, any more than the decision not to move forward on a 5e Dark Sun does - it's a unilateral publishing decision.
They're not asking a question, they're making a statement: "These are going away. Here are our reasons and here is something we think/hope will make up for it, but they're going away regardless."