There is an enormous amount of open research on hypersonics in China. Anyone saying China's not being transparent about their work or is a surprise is pretty silly, tbh. It's published regularly in scientific journals!
We're talking about the US Congress that forces systems on the US military that they don't need. We're talking about a US Congress that were more concerned back in the 80s when the US had the most advanced ICBM, the M-X, in the world that the Soviet Union had "bigger" ICBMs than the US.
Yeah the US probably doesn't need hypersonic weapons because they have bases around the world. They didn't need Prompt Global Strike where they can hit any target around the world in less than a pizza delivery time of thirty minutes because they have platforms placed around the world that can delivery a 2000 pound bomb that can do the same job by lesser expensive means. But they're going to do it anyway because American culture says they have do it better and be more advanced than everyone else on everything even if they don't need it. The more expensive the project means more jobs to constituents so they vote those in Congress back into office.