PhDs are fundamentally different in the US vs Europe. 4 years after BS is really the bare minimum in the US and 7+ years is fairly common; wikipedia claims that

PhDs are fundamentally different in the US vs Europe. 4 years after BS is really the bare minimum in the US and 7+ years is fairly common; wikipedia claims that 13% of PhD students in the US decide to keep working on their PhD after 10 years.