Why does everyone say you're born gay?

Ok I'll explain as best I can. I don't if this can count as evidence for ity being genetic but my uncle (my dads brother) is gay, and I am gay, I think that does count. BUT we can't prove it because we don't know how many people are gay, this is because in older times people used to deny themselves as being ual, nowadays its more accepted but those people who do not accept themselves build fake lives around them. Give it 200+ years and it will be easier to test because ity is gaining more acceptance as the years roll by.