Consider: the US is a (somewhat) greenfield project, while the EU is a brownfield refactoring.

These sorts of refactorings take time, even more so if done by "committee". The good thing is that explicit interfaces have to be created thereby (hopefully) increasing adaptability and resilience over time.

The US was greenfield 2 centuries ago. It currently has a lot more technical (political?) debt than the EU. Some reforms are long overdue.