> There has to be something deeper to gambling addiction. If so, then what is it?

I believe that B.F.Skinner and his pigeons answered this question.

As a legend tells us, once upon a time Skinner's apparatus that controlled reinforcements for his pigeons got broken. But Skinner didn't noticed it and went home to sleep. In the morning when he came to his lab, he watched how a pigeon did weird things in his cage. The pigeon walked in circles, dragged one of his wings, and it was like the pigeon danced some weird dance. Skinner was very interested what is wrong with the pigeon, and it turned out that his apparatus gave random reinforcements to the pigeon all the night.

Pigeon pushed the lever, and sometimes it got something crunchy, but mostly it didn't. Naive person might think, that it would lead pigeon to get frustrated and tired from the lever, but instead the pigeon doubled down and... Let me anthropomorphize to make things easier. It was like pigeon invented all kinds of omens and rituals to make the lever work. Like "I dragged my wing last time when lever had worked, so I'll drag my wing next time...", "ohh, it didn't work, lets try again, and again, ..., Yeah! it worked again, now I was standing on one leg, it seems to be the key to success".

Skinner was very intrigued and he developed "variable ratio of reinforcements", which led him to sharpen his methods and he easily could turn a pigeon into a maniac that push lever obsessively and just can't stop. One of the key findings was that less frequent and seemingly random rewards working much better than deterministic rewards on each push of the lever. When lever "just works" pigeon gets as much rewards as it needs and then goes to sleep. But when lever works sometimes, pigeon pushes the lever more and doesn't stop when it got all it needs.

Why brains do this to animals? I don't know what psychology thinks about it, I think that there are two possible (not mutually exclusive) explanations:

1. curiosity, a drive to learn how to control the reality around you. Maybe if you spend more time with the lever, you will learn how it works? Maybe you can learn how to get higher frequency of rewards? It would be beneficial.

2. it is a mechanism to create seeking behavior. If you get reward when doing something, then your brains would better believe that doing this is an interesting pastime. If rewards are rare, then your brains need to believe that it is a very interesting pastime, or you'd get bored in no time and die from hunger.

When I was teen I often went with my father to pick mushrooms in the forest. It is a pastime which teaches you in no time at all to look everywhere for mushrooms. You can chat, but your eyes constantly searching the surroundings, your legs wander around to look behind or underneath of bushes. Now, when I'm in a forest, I habitually look for mushrooms, I feel urge to wander off the trail to check on something looking like a dead leaf: maybe it is a mushroom? This behavior is beneficial for animals and the ability to develop such a behavior is beneficial also. Gambling just exploits it.