The US has tons of culture, both exported and not, and definitely distinct from other cultures.

If anything, US culture differs from others in that the story/identity of the culture is relatively rootless. The American Dream is based on the idea that your heritage can't define who you are, and the rise of post-war consumerism also significantly changed the story of the USAmerican.

That doesn't mean there isn't culture being done (guns, milkshakes, jazz, jeans, Florida man, Burning man, tech bros), it just means that where other cultures find identity in their deep heritage, the US has made a point of not doing that. Which comes off as shallow from their point of view, and narrow from the US point of view.