And the other reason might be that they really need the money for something, like buying something important for their life, or saving money or whatever, and actually I admit that the winnings are entirely your right and it's up to you to share some of it with others to party or to celebrate your winnings or not at all, all the choices are yours, But what I would suggest is that if you don't want to share any of your winnings with anyone then it's definitely better to keep it hidden and never tell anyone about it, because usually if you do tell and your friends want a share but you don't give it to them then it can cause problems in the relationship.
Buying something important with money from gambling. True doh but it is still not an excuse you can tell them and they will definitely understand. An not even share everything but given the little you can give is not baf at all. I don't know for others but its a thing of joy to me to always give because when you die you are not going anywhere with anything. For does that have such mindset should reconsider. And have a change of mind.