I read that R. Zera fasted one hundred days to forget the Babylonian Talmud before he left Babylon to live in the Land of Israel. Why would he do this when I've understood that the Babylonian Talmud is generally considered "better" than the Jerusalem Talmud? Indeed, the Talmud Yerushalmi seems to be pretty much ignored by the vast majority of people. When people say Talmud it's assumed they are talking about the Bavli, as if the Yerushalmi didn't even exist. This is simply the impression I get from frum Jewish society.
ר' זירא כי סליק לארעא דישראל יתיב מאה תעניתא דלשתכח גמרא בבלאה מיניה כי היכי דלא נטרדיה
and before starting he spent a hundred days in fasting, in order to forget the dialectic method of instruction of the Babylonian schools, that this might not handicap him in the Land of Israel (Bava Metzia 85a).
Just so it's clear, the main question is why would he want to forget what he learned in Babylon?