User blog comment:Bluefox87/Question. What was the point of Ignell and the other making antibodies for the dragon slayers really?/@comment-7418318-20160301100242

I have three possible (very likely in my opinion) reasons with what we know and can infer:

If this behaviour is a result of his change that's more than enough reason to make sure the other DS won't go through the same process and risk them going mad in a similar way.
 * 1) As far as we know as a Human Acnologia only wanted to wipe out Dragons. As a Dragon he clearly has become a being that will kill anything and everything if the mood strikes him. He intentionally hunts down both Dragons and Dragon Slayers, but as we saw on Tenrou he doesn't mind killing Humans one bit and likes to play/torment them before killing them.
 * 1) Acnologia lived for more than 400 years. Any person he forms a relationship with would eventually grow old and die, leaving him alone again. Sooner or later the DS would stop making friends with anyone other than themselves, leading them to a rather lonely life. Not something parent usually wish for their beloved children to have to go through.
 * 2) With Acnologia being a bit of both Dragon and Human, it's quite likely in my opinion that he can't beget children with either species, rendering him effectively sterile. The vast majority of Humans wants to have children at some point and it's even a natural instinct to pass on your genes. Being unable to do that isn't a fate that parents would want to push on their children.

Apart from that we have no idea what kind of changes the Dragonification had on Acnologia. There might also be a chance of it not working for 100%. Imagine if only part of a DS's body changes, like having a mostly Human body, but the left arm and right leg looking monstrous. Or a Human body with a Dragon's head.

Not to mention that we have no idea if Acnologia was able to transform at will from the start. For all we know he might have been stuck in Dragon shape for 3 centuries and only learned how to transform back into Human shape 100 years ago.