As for private infrastructure, private investors are happy to cut all kinds of corners. It's all about profit, preferably short term, than making something lasting, and even less so, about being proud in it.
The funny thing is, not very long ago (well, 30 years or so still) people were awestruck going into the US from Asia, Europe, etc. I've visited the US many times in the past decades, but I was more impressed with the past artifacts (e.g. Route 66, Chicagoan art deco, the fabulous country side, old New York skyscrapers, New Orleans, etc.) than with modern infrastructure. Heck, third tier cities in Europe have better subways and airports.
(That said, I did appreciate the abundance of ultra-cheap consumer electronics compared to old Europe).
The other thing I think (not an expert) is too much bureaucracy -- all the busy works laws and regulations that quadruple the cost of any project, and not in a good (e.g. public safety, long term quality, etc) way.
What's funny is the US budget is still huge. Just the stuff going into military BS could provide for top notch infrastructure, and even create an environment that could still jobs from China with a better supply chain (though, of course, the US can never account for the sheer number of Chinese workers).