This or that game having or not having something isn't really much of an argument (But if you want to play that way, as the previous poster said, there isn't much precedent when a job only exists in not even a regular main series game, but rather a remake of one). To be blunt I think they'd be doing a lot more than one FF fan a great service by using another more famous job like blue mage, time mage, or dark knight.
The thing is Necromancers are generally evil in fantasy worlds, with the most notable exception being Diablo II, but even in that game world, most necromancers certainly are evil, only the one you happen to be able to play isn't (wholly) evil. This makes them not fit in very well in a game where you aren't really playing the bad guy.