Gambling companies have a responsibility to protect children and gambling addicts. They should not advertise on posters in poor towns and villages because people there have money problems. If they advertise in rich cities they should avoid schools and youth clubs. Gambling ads are a part of daily life for people who do not want to gamble.
You are absolutely right, and I would even add that gambling establishments should not only not place their advertising, but moreover, they should prevent even the slightest chance that children from poor cities or villages can become addicted gamblers. And this should be achieved by the fact that schools in such regions should conduct additional courses after school, at least for a few minutes, where the teacher will at least briefly talk about the harmful effects of online casinos or sports betting on immature minds.