Every TV show leans on tropes to fill out their season. For the standard dramatic hour, it's brilliant doctors/lawyers/cops with a complicating flaw. For animated sitcoms, it's copying The Simpsons or copying the copies of The Simpsons. And for critically acclaimed premium cable, it's so many naked breasts.
That's why network shows pioneered the holiday episode. If you've got 23 episodes of funny! to do from fall to spring, it makes life a lot easier when Halloween, Thanksgiving, Christmas, Valentine's Day, and even Groundhog Day give you jumping-off points.