For more or less the same reason Hades himself was: it was his job. If there's a river that you can't Ford or swim across, there has to be a ferryman. Charon was that ferryman.
Charon, the ferryman of Hades
Hades has a boat full of Charon.
Hades is the ruler of the Underworld. Charon (not a god) ferries the dead across the river Styx into the Underworld.
Charon.
Charon was the ferryman of Hades.
Charon, The Ferryman.
His name is Charon.
Charon .
Charon
The ferryman in the Underworld is known as Charon.
percy bribed charon and promised to ask hades about a raise in his pay
Charon was not a Greek god- he was Hades' ferryman down the river Styx. He did not die.