Prohibition policies were not useful in any way in reducing the spread of addiction among gamblers, especially since gambling activity can be practiced on any game locally without the need at all for the presence of the state or one of its institutions to regulate.
You're right because if prohibition could have been the way out to solve every gambling addiction then those that would have first supported this are the governments, because they wouldn't want the people to be that involved in gambling, meanwhile that is not the problem about addiction in general, people also get addicted to other things aside gambling such as alcohol, food, women and other pleasurable things around us, so using prohibition policy is like stopping gambling itself all because of addiction which is impossible.