Why do they allow gambling to such extent when they already know how expensive it can be to the society? Why to allow casinos at the first place? It is because governments collect hefty taxes from this industry in order to let it run, the same goes to drugs and alcohol. If we expect the change, we need to be the change and start taking the first step so to let addicted gamblers come back under the category of normal gamblers who know and understand their limits.
While taxes play a large part in government and they will do many things to try and raise the tax income of the country. We also need to think about the people that want to gamble, or the people that enjoy drinking and smoking. Just because something is harmful for us doesn't mean it should be banned. For example, every year during summer people are drowning swimming in lakes and rivers. Should therefore swimming be banned? Same goes for gambling, most people can gamble reasonably without getting addicted, or drinking only on weekends without becoming an alcoholic.
We all have different perceptions to this matter, I get your point and it's also need to consider, there are people who can enjoy gambling without getting addicted and enjoy drinking without being labelled as addicted to alcohol.
People who knows how to limit themselves are those who are responsible enough to continue doing this kind of activities.
And on taxes, government both straight and corrupts are leaning to this side of market / industry knowing that it provides a good amount of collections, which we called sin taxes.