Gambling industry doesn't profit from people's illnesses, it profits from the house edge. In fact, if there were no gambling addicts, and, as a consequence, less governmental restrictions, gambling industry would only benefit from it. So, compulsive gamblers cause harm not only to them and their families, but to the gambling industry as well.
I fully agree with you, some countries ban gambling because of its negative effect like addiction, like China they are a country with the most number of population and if only gambling is not illegal in such country imagine how big it will contribute to the gambling industry, that would certainly make gambling sites more profitable.