Ruling rules

Good night Rabbi:
We find several ways of ruling that are ostensibly intended to "spare" a logical decision in a dispute, such as the rule that was followed by a rabbi other than Yael Kagam, and the halachah of a rabbi in Issurii and Shmuel in Mamuna.
A. Why doesn't the Gemara delve into the matter and decide on the opinion that seems more logical? Did the Gemara investigate, and these rules are just a sign to remember when the halakha was as to whom, or are the Amoraim unable to decide between the divided, and therefore determine that the halakha is always as to one of them (because he was an expert in the field, more wise, [more respected?]…)?
on. If this is indeed a solution to situations in which the Gemara fails to decide, how does the Gemara decide who to go with?
Of course, there are many rules and the rabbi cannot address all of them, but I would be happy for him to address the rules that I brought up at the beginning of the question.