It’s a lot easier for a business in one US state to expand to another one, but cross border business expansion in EU is still difficult.
People speak different languages, bureaucracy is different and often in a different language as well etc.
On top of that businesses are a lot more regulated than in the US.
I am honestly curious who you are pointing at (in particular if you exclude British leaders)
Partly because I am actually curious, I don't doubt there are bad leaders.
But partly also because, without any details, this is a very general trope, that I don't really think is very healthy at the moment. Since it is food for right wing extremists (you probably know yourself where some politicians in USA originate from).
bad policies: massive tariffs, extreme spend of the military-industrial complex at the cost of education and healthcare, a completely pointless War on Drugs that just increases violence (to be fair, many states have more or less legalized cannabis at this point), war in foreign countries (if all the money spent of Afghanistan had just been distributed back to American taxpayers in the form of either tax cuts of stimulus checks, how might that have affected the economy?)
bad leaders: I think most historians would agree that president Trump is not exactly Mount Rushmore material
bad deployment of capital: at the state level, this would mirror 'bad policies', ie I don't think war the Afghanistan/war on drugs was a net gain for the US taxpayer. On the private side, the boom/bust nature of tech investments - how many were buying Pets.com stock in 1998? How many people bought trendy NFTs in 2019? How many completely unviable businesses get funded today just because "our product has AI"?
so there might be other factors.