> Lonnie Golden, a labor economist at Penn State, said in survey after survey, American workers tend to say that making more money is a higher priority than having access to more paid time off
This is close to answering the question, however, it does not address why there is no national PTO law. It explains why workers do not take time off.
> Beyond that, Golden said, there’s always been an American discomfort with leisure and time off, and a cultural bias to display our commitment to work as a sign of status.
This is closer. As with the first example, this is just explaining why individuals choose not to take time off.
The answer is the USA is reluctant to put mandates on employers that would interfere with free association of entities due to our founding being largely influenced by the idea that individuals should be free to make contracts between others. The federal government is also limited in the constitution to only regulating interstate commerce. There are of course many examples where the federal government has ignored this thanks mostly to Wickard v. Filburn (1948).