If you look at the top supercomputers, US national labs occupy most of the top 10. But they aren’t enormously larger than the others. They are also built of out of standard parts. I’m surprised that they are recent, I expected the government to be slow and behind.
What do you expect US government to do with lots of computing power? I wouldn’t expect military to need supercomputers. Maybe the NSA would have a lot for cracking something or surveillance. But the big tech companies have more.