1. There would be a backlash for outlawing it where it was already legal, and hence had an industry depending on it. In fact, there was an option to even legal

1. There would be a backlash for outlawing it where it was already legal, and hence had an industry depending on it. In fact, there was an option to even legalize it in places so long as they did it within a year. 2. Enforcing it at the federal level costs money. It's easier to pass a ban where you force the states to pay the costs.