Pain in the butt if you've just climbed Gagazet to fight you-know-who, fancy summoning Ifrit for a nice 9,999 hit and... nope, nothing. Meanwhile, Issaru is just visiting Kilika and is using Ifrit to have a nice barbeque on the beach...
I'd PAY to see that.

My theory is that the fayth can probably send itself out to more than one location, but it is unable to face itself in battle.