If not talking about the first time loss gamblers that later become addicted, what you are saying is not completely true. If we can do a survey of gamblers that won or lost in their first game, the people that will chose won can not be 100%. They might not be 70%. It may be 50%. Some people will gamble for the first time and lose and continue to gamble. The main reason is because they think gambling is a way money can be made. Unless they change their the way they think about gambling, that gambling is is not a money making means, first time win or loss is not necessarily the cause of their addiction.
The story will be different for different individuals, some gamblers, the reason for their addiction is the first time winning trap as it becomes a trap for them as they weren't prepared for winning so they think winning when gambling is very easy and continue gambling until they become addicts. It's dangerous when individuals that keeps winning think they can't lose and that's what winning does to most of the individuals gambling.
While other individuals, the reasons for their addiction is as they're not disciplined individuals in life so when they start gambling with that same attitude, it becomes a disaster. When an individual wins he still can become an addicted gambler and also when he loses he can become more addicted to gambling due to him chasing after the his losses and trying to win back his money with revenge gambling. Many individuals don't use the money they can afford to lose when gambling.