it's because you are now a SMN, if you want to use carby (why as a SMN you would need them as Ifrit, titan, and garuda, do the exact same things if not better) you would have to remove your soul stone and revert to ACN again.

also the icons don't change for SCH either and tbh its really no big deal, why would you want so many useless Icon's when the set summon icons work just fine? they each represent a different version of a summon one geared to DPS the other to tanking (healing and DPS for SCH).

honestly with the wonky AI of pets you should be worried more about pet control then the icon used to summon your pet (no offense)