But they are paying, aren't they?
Advertisements don't generate money from thin air. Advertisements cause people to spend money they otherwise would not have spent. That's why companies buy ads in the first place.
And if you're showing ads to poor people, you're probably causing them to spend money they don't have.
It seems like the same is true of advertising. Yes, some people are spending money but it doesn't necessarily follow that they're people who can't afford it.