Another reason why they separate releases could be for more profit from the new costumes. Let's face it, the new Queen costumes aren't the greatest and they're definitely not as good as Ram Horn. If a player decided they want to buy 1 Halloween costume, they'll now go for 1 of the Queens, and there's a chance that if they release old Halloween costumes later that player will be like "Oh man, this costume is far superior! I have to buy more pearls and get it, it's limited time only!" So now they gave more money to Kakao.