it's probably the most profitable industry because gamblers will always come back no matter what is the condition.
no, though gambling industry is profitable but it's not the most profitable industry in the world since in some countries, gambling is illegal.
here are the list of top 10 most profitable industry in US,
https://www.ibisworld.com/united-states/industry-trends/most-profitable-industries/as you can see, gambling industry was not even included though in US gambling is legal.