Frozen
Liquid aether, as per Gabriel, increased the rate of his growth to the next level, while the additional aether simply dissipated from his body. Neither Nero, nor anyone else had any reason to believe that the aether absorbed from the liquid form could be actually used for abilities and cards.
Yet at the same time, considering the rarity of the liquid, it was not like they knew much about it, anyway. It was unlikely that anyone had tested it to be used like this, and Nero didn't mind being the one to do it. As valuable as the liquid aether was, it was not as valuable as his own life - at least to Nero himself.