Let me guess, some cis people with gender neutral names like Taylor and Alex and Kirby were being misgendered because of it?
Edit: well, the official reason is that there's a law that bans them from banning it, passed in 2023.
"may not require or prohibit a member of the armed forces or a civilian employee of the Department of Defense to identify the gender or personal pronouns of such member or employee in any official correspondence of the Department."
Guess rule of law isn't completely gone then.
^Just mostly^