It's usually like this because now that they have made such huge winning they would think is the right time for them to increase their bets sizes without knowing that things aren't done that way. But lemme just add something, "you can't determine a real gambler untill the win something mind-blowing" and of course you and I can't factor out whether they would make judicious use of their money or not but what matters is that they had made a life changing bet so therefore they must also try to use the winning to change their stories by doubling their bet ( only a foolish gambling could engage in such gambling behavior).
Gamblers are gamblers and new gamblers can stop their gambling activity any time like losing all bet capital or feel bored with betting and saw no chance of winning and getting richer. It is possibly very different with experienced gamblers who almost won't stop betting even after their big wins. They can wisely withdraw money of big win and continue to bet with original bet fund but I believe they will not stop betting only because of big wins.
It does not mean they are bad gamblers - as they already wisely withdrawn - but it is more like their degen instinct and also consider gambling as their hobby.