Here's why:

* Carbonic acid is a weak, diprotic acid.

* Diprotic means it can donate two hydrogen ions (H⁺).

* The IUPAC name is based on the chemical structure and the functional group (in this case, the carboxyl group -COOH).

While sometimes referred to as hydrogen carbonate, that name is more commonly associated with the bicarbonate ion (HCO₃⁻).