[selkin]

It's exactly the same reason: gram referenced a known quantity. Changing it by a few insignificant digits because of the kilogram update wouldn't force people to realign their perception of it.

Changing it to ~1,000 times what it used to be, or giving it a new name, would force people to realign.

There's reason many people still prefer customary and imperial units, and it's not just bigotry and nationalism (even if they play a part in that preference).