Why does the exhaust cam have the waterpump drive extension on it?

It is the intake cam on the left bank that has the water pump drive on it.

Former owner of '99 CSVT - Silver #222/2760 356/334 wHP/TQ at 10psi on pump gas! See My Mods '05 Volvo S40 Turbo 5 AWD with 6spd, Passion Red '06 Mazda5 Touring, 5spd,MTX, Black