Personally, I don't see the point in sharing winnings posts on social networks, unless the person has a personal gambling channel where he helps to understand gambling, communicates with the community and shares ideas, reviews, etc. And if a person publishes his winnings just for self-affirmation in the eyes of the public, it certainly does not make any sense (at least for me). Besides, such behavior carries some risks for underage users of social networks.
People's behavior is often irrational - someone buys a watch/car on credit that he cannot afford in order to brag to his friends, someone draws attention to themselves in a different way. Apparently, those who publish their bets (wins or losses) have found their niche and in general this is understandable - if they are involved in gambling, then this topic is of interest to them and it is natural that they will make publications in this area.
For example, I don’t like some things, but I understand people who are fond of them, I remember that a couple of years ago some celebrity was exposed who had a “secret” account where she published methods for making onion rings. Sounds pretty weird to me but I can understand it.