And I get that - in fact I live it. I'm a government contractor that works on transportation projects and it's frustrating when a particular agency doesn't want to use an innovative technique or design that has literally been successful on another project that's only a few miles away but project managers don't want to be testifying in front of their state legislatures about wasting tax payer money with a new fangled approach when the tried and true could have been used. Magazines like Engineering News-Record and ASME/ASCE journals bang the drum for concepts like "state of good repair" and ROI, but as long as the public will hang a politician or project manager out to try for an unsuccessful project (or worse, a new technique that kills someone), project managers will route around risk.
Again, I'm not saying this is why US projects are so expensive, but there is often a rational through process behind seemingly irrational decisions.
(yes, there are times where incompetency and/or corruption are also to blame, but IME it's much less often than portrayed in this thread).
States make their own choices, though. The DOT can only cajole them by dangling money. If the only competency in a state DOT is to cut a check, and there is not going to be any price to be paid for putting in a road that is unsafe or that does not last or that costs too much, then it is more likely that too much money will be spent.
Another related story is this relative went to Germany to confer with counterparts over there and compare notes. The Germans were laughing at them because they use the US research, but the US doesn't. We have great research spanning multiple decades, but political concerns are what end up determining how roads are built.