Back during some of the early betas, the /wait command could take decimal points in order to match the cooldowns, but that made them too effective. SE changed that to add some extra time on macros in order to prevent them from being the most efficient way to do combos. The devs want manual control of each individual action to be the most efficient and effective way to play, with macros available for simpler things where you don't care about maximizing your effectiveness. If macros were the most efficient, then they would become nearly mandatory for difficult content and the devs don't want people required to play on auto-pilot.