Why do white Americans think they have no culture?

[WindowPhil]

Because what people refer to as "white culture"  is just mainstream American culture. Owing to the fact that nonhispanic white people make up 60% of the population and have historically been the group in control of U.S financial capital and mainstream consumerism. And there's no need to have a collective identity around being white since it's seen as the default in the United States.

Hip Hop is often seen as a "Black thing" while Hair Metal isn't really seen as a "white thing" (despite hair metal being heavily white). Because Black people are 12% of the population and haven't historically controlled financial capital. So something with a heavy concentration of Black people is seen as being outside the default. And white people who are outside of the American mainstream aren't seen as aspects of white culture. In that case, it's "Mormon culture" or "Southern Culture".

But that's not the only thing, American culture has been heavily exported around the world and has been seen as the global default for quite some time. Snobs in Europe ridiculously say America has no culture as they watch a marvel movie while wearing blue jeans.

So it's a combination of those. Being part of the default group of a country that's seen as the default country. Where non-mainstream white people aren't seen as white when they're outside the mainstream, but something else. While white people may have no culture based collectively around being white since they've always been a part of the American mainstream, that doesn't mean America has no culture or specific groups of white people don't have a culture.