The reason people do better is because step 2 questions are more predictable from USMLE world...because all step 2 questions are clinical vignettes, and there are only so many questions like this writers can come up with. So people can pretty much memorize 90% of the type of clinical scenarios that show up on the exam by doing the UWorld questions. Moreover, everyone studies hard for shelf exams during rotations, which have very similar questions.
So that is why people do well on step 2, not because it is a repeat of the basic science content of step 1. Maybe 2-5% of questions are pure basic science type questions, and up to another 10% will present a clinical vignette but ask you about some sort of basic science pathophysiology type of question.