Science was presented in a just-so way in our youth. It still is ( #Scicomms ), but back then, whether reading Junior Scholastic or the margin captions of a high school science textbook handed down ex cathedra, there was no communication pathway to pose vexing questions in a publicly visible way as we do now.

We don't even know if Miller or Urey themselves would have (or did) frame their results that way. The honest framing is 'hey this is one way to form amino acids, and maybe that pathway is reflective of the origin of life, but that supposition remains conjecture on our part.'