It takes a newly-elected government at least four months to install itself comfortably into the nooks and crannies that characterize the corridors of power. Selecting nominees for the many offices and committees that usually need reconstituting - due to executive privilege, or resignations of holders with viewpoints opposed to the incoming administration. Vetting procedings, as well as general familiarity with new official environments, rearrangements and general euphoria that characterize accession to power, take time to settle.
In my opinion, the last four months of the year are just the right time for such elementary proceedings. Which is why elections should be held earlier; in August preferrably, so that by January of the following year, everything is set for a neat take-off. Voters allow themselves the chance to bond over the festive season, and easily overcome the tensions of a charged elections season. Schools and businesses can look forward to a complete new year devoid of distractions, when the festive season ends; and the new year has a psychological starting point from which to evaluate its progress.
When the country votes in December, just the opposite happens. Nobody really has a festive season, as the days are consumed by political tension and noise. These spill over into the new year, and literally waste away the first few months, as a new government strives to install itself, while meeting the challenges of a demanding public. In temporal terms, two calendar years are lost to politics. Should schools be opening, or should we await the Supreme Court's ruling on the presidential election? Should you, instead, be flying away to the holiday you could not award yourself due to your civic commitments over December? It is unnecessary messiness. And it wastes the natural tendency of people to work harder towards the end of the year.
Every time you mix two high-tempo seasons, someone is bound to come out a loser - either emotionally or even economically. That hurts the nation, deeply.