If you go back and read prior patchnotes posts from KI it will give you a clue as to why, mainly due to the customizable nature of pets now they don't have a standard price or standard look/traits/etc. So now they are only available via shops to buy and sell.
The only problem would be the traits, which could go back to baby if you put it back in. Really, the pets that make hybrids were not auction-able anyways.