As I noted at the time, it is unsurprising that this is the case as this only happens when there is a natural hormonal imbalance or (more often) the Axolotl has been forced into the metamorphosis through limitation of diet, adulteration of the water in its tank with chemicals such as iodine, or other such measures.
Moreover, a metamorphosed Axolotl has a significantly shorter lifespan than do the neotenic adults.
@ThylacineAlive There was a metamorphosed form of the axolotl kept for a while in the reptile / amphibian house of the Chapultepec zoo in Mexico. This is the only one that I remember being kept in a zoo that I can think of.
From what I remember this individual did live much longer than expected for the adult form of this species but it has almost certainly passed away by now.