That is a strange but understandable misunderstanding of the relationship between the Federal government and the States in the US, it is not remotely like Germany. German states are much weaker both in theory and practice. The Federal government often cannot intervene unless the States ask them to, and the States control the terms of that intervention. People raise this issue in every major natural disaster under every administration, baffled why the Federal government doesn’t do more, oblivious to the legal and practical structure of the US government. In my own lifetime there have been many cases where States actively restrict Federal operations within their jurisdiction, with full support of the Federal courts.
By convention, the States typically allow the Federal government to operate freely within their jurisdiction, but it is not an obligation as it is strictly at the pleasure of the State. When there are strong disagreements between the Federal and State governments, this is a major point of leverage. Many Federal programs have been successfully killed by States prohibiting Federal operation in their States.
I'm very familiar with the constitutions of both the United States and Germany. From what you're saying, I strongly suspect that you're only familiar with one of them.
The German Federal government is highly constrained in what it can do in many areas of life, because those areas are under the control of the states. This is why there are 16 different high-school diplomas (Abitur) in Germany, for example.
Formally, there is a strong division of powers and responsibilities between the federal and state level in both countries. But in both countries, the Federal government wields a great deal of informal power. The Federal government has access to much greater financial resources, which it can wield to coerce states. My personal view is that this Federal power is even greater in the US than in Germany, due to the enormous political power of the President and the greater financial power of the US government (Germany has to deal with the ECB, while as Trump has shown, the President can directly bully the Federal Reserve).
If Trump had made strong statements about the need to impose quarantine measures early on, that would have had a big effect. There are many instruments at his disposal that he could have used to coerce recalcitrant state governments with. Instead, he downplayed the virus until mid-March, and has continually argued against the shutdown (see his Twitter thread). In Germany, Merkel met with the state governments, they agreed on a set of common measures, and she gave a televised address explaining those measures. She's been pretty consistent in her messaging, unlike Trump. Maybe that's because she's a physicist, and he's a real-estate mogul, or maybe it says something about what plays well in each country.
I was born a citizen of both Germany and the US and have worked in both countries. Using Germany as your exemplar was to your disadvantage. I have also worked internationally for the UN, and with multiple major governments at a high level. I am under few illusions.
That aside, you did not actually provide evidence contrary to my assertion.
You vastly understate the power of the US Federal government when you compare it to the EU, and understate the power of German states. I don't know what you mean by "evidence" here. We're not discussing some sort of experimental result. We're discussing the basics of the American and German constitutions.
By convention, the States typically allow the Federal government to operate freely within their jurisdiction, but it is not an obligation as it is strictly at the pleasure of the State. When there are strong disagreements between the Federal and State governments, this is a major point of leverage. Many Federal programs have been successfully killed by States prohibiting Federal operation in their States.