https://archive.org/details/minecraft-game-design

According to Vanilla guidelines, all animals are gender-neutral. This means that every animal has the most distinctive features of its species, for example all bees having stingers when only females have them irl, all cows having both horns and udders, etc.

a distinctive feature of deer is their antlers, so this should be applied to all deer, not just some of those which naturally spawn.

Reindeer are one of the types of deer that have both genders having antlers, although this would be voided by the base deer having horns - maybe both mobs could be unified.

No, this was a conscious design we made.

Yes, Minecraft is gender neutral, but we do not follow this book exactly, and despite 50% of Deer not having antlers, they are still gender neutral. There are no other aspects of gender present, and they can all breed with each other. Antlers (and the lack thereof) are an important part of real Deer's visual identity, and are much more noticeable and have an effect on the look of the animal far more than things like stingers, udders, and small horns, which is why they are kept.