I feel like because the gambling commercials/content are annoying (hell, I've been betting on sports since I was like 10 years old) and I find them annoying people are making a wayyyy bigger deal out of gambling than what it is.
As Abom said - anything that gives you a hit of dopamine can lead to addiction; for some people that can be shopping, video games, gambling, food, ect.
It's a new industry so these companies are spending on marketing to attract customers but it will settle down after a few years.