Of course, it is also a challenge, but at least we can change it if we really want. But those who claim they can't are those who already have in mind that they can't change themselves. Our minds can manipulate our actions, and if we can control it, we're certain to become responsible gamblers.
Maybe those that have said so have already tried but it didn't worked for them. Self control is hard to maintain when you're so distracted with a lot of things like with everyday internet life.
And that's why they have given up and have already said that they can't change themselves. The mindset is what they have to change for as long as they will believe that they can no longer change, that's how it will be for them.
But like what you have said, we can control and manipulate our minds that even we can't do it but if we're telling our heads that we can, we can change, we can control ourselves.