you confuses theology/doctrine and discipline.
doctrine does not change. theology expresses doctrine as much as human can. theology changes in expression as human develops in (supernatural and natural) knowledge and understanding.
discipline (where more fasting rules and outward signs people notice belong to) changes with society and also in connection with the secular world, and also people-to-people.
Eastern churches keeps the lent not only on Fridays but also on Wednesdays, while Westerns not. are there theology disagreements? not at all.
it's like saying "look how funny computer system design principles are because it's implemented in dozens of different instances to suit users needs"