For most people, no, it's not the only reason. First... none of those markets can even begin to approach the ubiquity and profitability of the drug trade. We are talking billions of dollars flowing among hundreds of millions of drug producers, sellers, and consumers. Second - and more importantly - all of the examples you listed involve crimes with victims. Producing, selling, and using drugs are all inherently victimless crimes: no person is harmed or deprived of their rights as a consequence of these actions.
Criminal organizations make the vast majority of their profit from the drug trade, because the market for drugs is huge, but they engage in many other crimes as well, including the ones you mentioned. If we can deprive criminal organizations of the profit they make from drugs, they will inevitably be weakened - their ability to use money to influence and bribe corrupt government officials to their ends will be reduced. No doubt they will redouble their efforts to make profit from other markets, but the markets for the things you mentioned are nowhere near as ubiquitous as the demand for drugs is (and there is no reason to believe that criminal organizations aren't already trying to maximize the profit they make from these other ventures.)