Addictions are about enjoying the thrill of the activity.
People who aren't addicts tend to look at the consequences of their actions and choose to stop. While the addict's focus is on the high they get from the experience itself. It's not about results.
I would imagine someone who is addicted to gambling simply believes they're going to through a "slump" or are having some "bad luck". Being addicted to "hope" or luck can delay needed changes.
Ultimately they believe if they keep betting they'll have a chance to win it back! The thought of "quitting" in their eyes is the same as giving up their dream. They'd feel like they've "invested" all that time & money and got (nothing) in return. They don't want to give up!
I've observed people who have been in "toxic relationships" do the same thing! They'll tell you they've been together for 10 years and simply refuse to walk away because it would mean that those years were wasted. They're holding onto the hope things will change.
The concept of them "wasting additional years" never enters their mind. Similar to the gambler he believes (eventually) it will "payoff".