Theme. Their are several spell-casting classes that all might decide to go into illusions.
Furthermore themes are all about your accessoires. Weapons, equipment, spellls, tactics. Illusion spell fit the line perfectly.
Class, class, class!
Necromancer as a class too, while we're at it.
The rest of the wizard variants (Conjurer, Diviner, Evoker, etc.) aren't really distinct enough and can easily be lumped into general Wizard/Magic-User.
Lan-"Illusionist - best class ever!"-efan
EDIT: is there supposed to be a poll with this - all the other class threads have one...
Doesn't the 3e rogue's sneak attack suffer from the same problem? It happens to be not useful in much the same situations as illusions too - fighting mindless undead, constructs, plants, and the like.Personally, I am against such overspecialization. Just like fighters who only use swords, a mage who only uses illusions has too many situations where their abilities aren't useful. And if you aren't using illusions, why bother with being an illusionist?
Doesn't the 3e rogue's sneak attack suffer from the same problem?