Hello,
I think this feature was added later (maybe in BC or WOTLK? can't recall, was too long ago), it would be a very good QoL feature to have a buff for a few seconds when resurrecting in a BG that allows to cast spells for free in order to re-buff.
Currently, with both my mage and priest, rebuffing me when I rez puts my at half mana which means I have to drink for at least 15-20 seconds after rez in order to be able to fight.