"Which is an excellent question. The problem is of scale. A beginning wizard could at best disable three enemies before having exhausted their repertoire of spells for the day. In the encounters we typically engage in, that is so small a difference as to be nonexistent. Silent and generally static illusions are available at that level, but similarly limited. Permanent blindness is available at the next level of spells, but again, is limited in scale. It might be possible to develop a mass version of such a spell, but it would require far greater skill in wizardry to cast."

The fire is a weak spell cast by a very capable caster. Of course it appears powerful!