This doesnt make sense at all. VH is easy to implement and is one of most popular races. There is absolutely no reason not to include it in the game.
I think Larian may have two reasons:
1. Balance. VA is very strong. When 5e came out it was already regarded as potentially the strongest race, easily fitting any class and allowing an early feat. The feat can be an absolutely game-changing boon, few races give you features that can even hope to compete with a free Sharpshooter or Polearm Master at level 1.
2. Discouraging people from playing humans. I'm sure I recall Sven saying it's disappointing for them to see so many people playing humans when they put so much effort into the other races. Perhaps they hope there'll be more tieflings and dragonborn if humans are unattractive gameplay-wise?
This is all guesswork on my part and I'm not defending these reasons, just thinking aloud. I'd like VA to be an option, though if they're reserved about balance I can only commend them for that.
