Perhaps when choosing to gamble, athletes are searching for something that is missing in their lives, such as excitement beyond what they get on the field. While their careers are already full of challenges and adrenaline, maybe some of them found themselves addicted to the added thrill of high stakes. Outside of sports, the asides add a lot more color and texture to the description.
It is also possible that some athletes get bored or feel suffocated by the immense pressure in the wake of expectations that come hand in hand with their careers. Gambling can be an avenue of escapism or a route to feel re-empowered in control in something in their lives. Alternatively, overconfidence or simply believing that they are immune to being caught is also potentially motivating.
But this choice… understanding of the true value of their career and reputation. Money can be earned back, but a good name and legacy are hard to restore after being tarnished by a scandal like this. This can destroy not only their career but also the trust and respect built over a lifetime.