There are millions of people who are equally as lucky as Bill Gates in terms of family economic and social status. Luck plays a role but it is not the defining factor.
"Millions?" How do you figure? Gates was born well into the top 1%. Tens or hundreds of thousands is more accurate. Luck isn't the deciding factor, especially in what endeavors to pursue, but it is a prominent factor in the success of those endeavors.
Let's say you are right that he was born into the top 1% in the US. I am not confident that is true without data but let's say that is it for the sake of argument.
.01 * 330,000,000 = 3,300,000
So yes, millions. And yet there are only a handful of Americans like Bill Gates.