WotC has been very clear about their goals with this edition, which include better serving fans of previous editions and encouraging them to sample and convert. They deliberately chose to include all of the class/race combos from previous PHBs in order to appeal to the BROADEST possible audience.
If you want to see an edition intended to significantly innovate and carve out new space for the game, you need look no further than 4e. (Where separating out high elves as Eladrin is perhaps a similar innovation to the sort you're proposing.) Some folks liked that, some didn't -- but it happened because it was within the mission statement of the edition.
5e, by contrast, has a VERY different mission statement, and so we should not be at all surprised that nothing similar happened. WotC wants people who played half-orcs in previous editions to be excited to play half-orcs in the new edition. The percentage of people who will be stoked to play orcs instead of half-orcs *regardless of whether it's a good idea or not* is a tiny, tiny fraction of a percent.
And again, folks who actually like the idea of replacing half-orcs with rules identical orcs can totally do that without needing any support from WotC whatsoever.