See, declaring a #LeapYear was actually the decision of the #PontifexMaximus, which was an elected political position. If Pontifices Maximi would routinely declare a leap year if they liked the #consuls, and refuse to declare one if they disapproved, in order to prolong or contract the administrations of various consuls according to their own preferences and ambitions.
Plus, since a #LeapYear wasn't declared until late, outlying parts of the empire wouldn't know until months later.