I don't think that this is as a result of greed, basketball players are well paid and it's useless for them to chase money through gambling but some of them like this guy in particular is dealing with gambling addiction...this is the reason why he was ready to put his career on the line, he knew that what he was doing was am offense and it's prohibited but he still went ahead to do it, I think he was trying to show people how good he is
It was stupid that mostly contributed to his problem because he already knew the consequences of going against the rule but he decided to push forward, feeling like a god. He probably thought that he was not going to be caught that's why he agreed to take the risk and ended up to ruin his career. Either he was stupid and addicted to gambling too or he was just stupid.