Now that rabbit hole is fucking deep.
TLDR would be Japan created chicks with dicks and the west made sluts with nuts.
You see the original purpose of a futanari is not for procreation but purely for the woman to experience pleasure from a man’s perspective. Think of it as a sensory strap on with built in nuts.
So no balls would make sense and at the time (bible black era, 19forgotten, etc) was deemed superior for the following reasons.
1.) Is that no nuts = no kids! So its fun for everyone.
2.) Is that there’s easy access to the pussy.
I mean what are you gonna do tell her to move ya nuts or you gonna hold them so you don’t hit em?
Its a logistics thing! The futa can experience two perspectives at the same time!
The big fat futa balls came in around the 2k ish timeline and started from a western perspective. I mean who the fuck wants to animate a dick and a pussy in one skeleton? Shits hard and people are lazy. In which the no pussy one also came in. Its also kinda defeats the purpose of being futa (two) when you only have one out but whatever.
From an eastern pov a “newtype” would be the closest to a trans. The perfect and very first example would be Poison from street fighter. As some westerners cried abuse and other shit as to why a woman was fighting men in a fighting video game. I mean no fighting in a fighting game wtf? Amarite?
Now there’s also one more type which is more in the femdom/fantasy/magic shit where a witch curses you and your dick and balls can come off (non painful) and can easily be returned by just sticking it back like a magnet.
Now the fun part is other people can use your dick and you both feel the sensation the dick feels even when its not attached to you. I suggest not going any further because you might awaken weirder shit. There was only a manga source though.