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.
I think it is possible for this companies to control and limit their gambling ads to some specific demographics but it will be very difficult to achieve this completely because this guys that own this companies are into the gambling business to make money and that makes adverts one of their strength.
They know that exposing gambling to children and poor people makes them even more vulnerable but the truth is that those ads will always find their ways to reach those audience either directly or indirectly because there's limitations to how specific you can target a particular audience.
For ads like the public banner placements and other online banner placements, it will always cover a wider range of audience than intended including those people who don't want to see them. A solution that can help but cannot completely solve the problem is when governments take more stronger steps by imposing stricter regulations such as limiting gambling related banners near school, poor neighbourhood or market environments and it is also very important for government to enforce more of Responsible gambling so even the rich are protected from taking decisions that they will understand.