Because no other sensory input can change human consciousness so quickly and thoroughly. The smell of frankincense, for example, is instinctively known to be holy by all cultures. It is still used extensively in the Catholic church in the west. Special gold altars were built for its offering in the ancient Temple of Israel.
What is Incense?
Incense is unlike other kinds of perfumes because it is designed to spread fragrance to its target immediately, creating an atmosphere or setting a tranquil pace for whatever activity is intended. It is also infinitely more versatile than other perfumes, because it goes far beyond being just a perfume: good incense makes use of substances (tree barks and saps, roots, flowers and other botanical products) which cannot be liquified or isolated into a perfume or cologne. And in the burning, ingredients of extremely differing forms combine into a single, unique bouquet containing subtle tones or shadings. Incense is a kind of “mental stimulant” which can transform the ordinary into the very special, and do so easily and at no great expense. Fine incense burning in a plain room with gentle lighting and a few special artifacts can produce the setting that subtly calls the psyche to relax, lighten and flow with the moment. Whether the space is a temple or a bedroom, the effect is the same. A mood is set, and the moment takes on a heightened, special meaning.