Not just some gamblers. Majority of the problematic gamblers would probably not reveal to their friends and family that they are already addicted and are losing big. So friends and family should know how to read the signs.
I agree, accepting their addiction is one of the hardest part since it involves changes and others are probably afraid that if they tried to reveal their gambling issue it could potentially tarnish their reputation and relationship between their family and friends.
That's a good question, but I think you are right, people who have never win anything are less likely to get addicted than people who have won big prizes. When you've made good profits I think you start to think you can be lucky again and win bigger prizes than those you've earned until now.
This is somewhat true, I remember there was a comparison about a scenario where one gambler starts winning several times in a row compared to the second gambler who lost it all.