> If it's so bad for gamblers, why don't they stop?

Because they're stupid. Gamblers are idiots, gambling companies prey on the dumb. Anyone who understands the very basic math behind the games understands that it's pointless to play, you'll just lose more the more you play. That's the whole point. It's not even a secret, you can find the exact odds for each game.

Poker is different as you're playing other players rather than the house but it's still a negative sum game as the house takes a cut so you have to be better than the others to play. And if you're a reasonably intelligent person you'll just bet a little and accept your losses and move on. Or not play at all. Idiots will do dumb stuff like bet way more than they can afford, then they won't have money to pay their mortgage, rent etc and so on. People call it an addiction but I'm pretty sure it's mostly just being really really stupid. Can't be addicted to gambling if you aren't dumb as a rock.