"Back then" in the olden days ... it was the same. Voting was done prior to playoffs.
Things were just viewed differently back then, prior to people understanding numbers like they do today.
Carter was the primary run producer on a prolific offense, I believe 3rd in the AL in RBIs, and that stat carried a lot more weight back then in the eyes of voters. Almost like RBIs were a sign of how clutch you were.