Fortunately with practice, it's surprisingly easy to make incense. Therefore combustible incense can be burned in the form of bricks, cones, sticks and other shapes, whereas noncombustible incense must be sprinkled onto glowing charcoal blocks to release its fragrance. Perhaps because it's easier to make.
Herbal magicians are notoriously practical people.
Since cone, stick and block incense burn at steady rates, such effects are impossible with their use. The advantages of combustible incense can outweigh its drawbacks, depending on circumstance. You could take out the censer, a charcoal block and the incense, light the charcoal, place it in the censer and sprinkle incense onto it. Or you could pull out a cone of money-drawing incense, light it, set it in the censer and get on with your ritual. Different magicians prefer different types of incense.