This paper [1] backs up your hypothesis. "First, crack can be smoked, which is an extremely effective means of delivering the drug psychopharmacologically. Second, because crack is composed primarily of air and baking soda, it is possible to sell in small units containing fractions of a gram of pure cocaine, opening up the market to consumers wishing to spend $10 at a time. Third, because the drug is extremely addictive and the high that comes from taking the drug is so short-lived, crack quickly generated a large following of users wishing to purchase at high rates of frequency."

This DEA History Book [2], however, suggests the reasons might be partially economic. "Soon there was a huge glut of cocaine powder in these islands which caused the price to drop by as much as 80 percent."

[1] http://scholar.harvard.edu/files/fryer/files/fhlm_crack_coca... [2] http://archive.is/1wF5