> Why didn't some other country at some point run some studies
I know little about the topic, but I can suggest reasons why this isn't so simple.
Up until the 1960s or so, people didn't care much about pollution. They thought nature could absorb it. This include Europe. The Swiss chemical industry dumped their wastes into the Rhine, and they weren't the only one along the river.
The goal then, in Europe as in the US, was to make money.
It wasn't until REACH in 2007 - https://echa.europa.eu/regulations/reach/understanding-reach - that laws were changed to place the onus on companies. Quoting that link: "To comply with the regulation, companies must identify and manage the risks linked to the substances they manufacture and market in the EU. They have to demonstrate to ECHA how the substance can be safely used, and they must communicate the risk management measures to the users."
However, for reasons I do not know, PFAS were excluded from REACH.
My guess is it's for the same reason - PFAS are industrially very useful. Europe's chemical industry is about the same size as the US's, and I know it can influence legislation there too.
> Congress needs to do its job and stop blaming SCOTUS for federal law interpretation
My point was that "a nice excuse for inaction" is insufficient to explain what's going on in the US.
> Constitutional law is a different story because Congress can't do anything about that
My example about the EPA power to enforce Clean Water Act was a constitutional law issue.