Illusionists are lazy

Shaping reality takes alot of mental effort and energy, just ask a healer. They tire faster than other magic users because of the effort required to make their forced realities "stick"

Which brings us to that obscure path of Illusion. What is an illusionist and what do they do that makes them different from other magic users?
To put it simply, they're lazy magic users. Illusion is a philosophy, not a path. Somebody calling themselves an illusionist is usually not wholly devoted to a magical path. Their shaping of reality is not designed to stick, instead it is merely a means to an end.
For example: A wizard would place a warding on a building to prevent entry, whereas an illusionist would just make the building disappear. The Wizards method is more absolute, nobody but the Wizard can enter. At a high price though; he now has to devote energy and attention to maintain the warding. Whereas the lazy Illusionist just spins a web (the Illusionist lexicon for matrix, it has some link to the way a spider catches a fly in its connotations or somesuch...) and drip feeds the spell some energy to maintain itself. As you can see, they've both achieved the same goal but via differing methodology.

A reason the illusionist is reluctant to use more divisive magic is because they are more than likely pursuant in another path other than magic. This is why their methods are usually quick fix while not being permanent solutions. Some Sages follow the illusionist philosophy, reasoning that it frees up more time for other studies.