There are many people like that, and they are winning their bets, maybe we can say that they are really lucky, but I think it is also because of their experiencce as a sports bettor. And even if you are an experienced gambler, there is no way that he will win every single match he bet on, I think there are still some bets that he lost.
I also don't have some friends or relatives or I didn't heard all about a person became rich because of gambling. Many people that I know experienced the reverse of it. They are rich because of good business and then when they enter the world of gambling and didn't control themselves they end up poor. Gambling isn't the best way if you want to become rich because in gambling the percentage of earning is not determined.