i just told my uncle about bitcoin today. told him a few things about it, and instead of asking more, he wrote it off as a scam. he compared it to a forex ponzi scheme that my uncle-in-law fell for. he's got quite a bit of his money in stock, yet the whole idea of a decentralized seemed so foreign to him that he just wrote it off without asking more 
You're probably not a credible source of information for him. First of all, your uncle is older than you and when people are older they generally tend not to take advice from younger people, because they already have their own view of how the world works, and may feel ashamed of themselves if they think they don't know something that youngsters do, so they are pretty rigid in their beliefs. Sometimes it'd literally take a total crash of their beliefs for them to become more flexible and even then it's hard to do.
Second, 'no prophet in his own land' applies here, meaning that family members are unlikely to trust their own kin in such matters.
I am sure, that if your uncle heard about it from some credible source, like a newspaper he trusts, or his old buddy, he'd at least take another look at bitcoin and give it a try to understand what it is and if it's worth investing in.
