His unfulfilled dreams could also contribute. Naruto has big dreams for the ninja world and for himself. If in the fanfiction some of these dreams are still out of reach, they could be on his Christmas list in a sad way. For instance, if he dreams of a world where all ninjas are truly equal but that hasn't happened yet, it would be a sad entry on his list during Christmas.
Maybe it includes the names of his lost friends. Since Naruto has lost many important people in his life, their names on the Christmas list could represent his longing for them during the holiday season.
Christmas stories can be sad because they might highlight the loss or absence of loved ones. It also might show the pressure and stress that come with the expectations of the perfect Christmas, which doesn't always materialize.
One reason could be for the sake of creating drama. Writers might blame Naruto in fanfiction to stir up conflict and make the story more interesting. For example, they could make him the cause of a rift between other characters.
Naruto could ignore fanfiction because it often contains elements that are not part of his reality. The fan - made stories might distort his character or the relationships he has. For example, some fanfiction might pair him with characters in a way that doesn't make sense to him or goes against his values, so he just ignores it.
It could be that the cultural aspects of Christmas don't resonate with Naruto's character in the fanfiction. He comes from a different cultural background in the Naruto world, and the whole idea of Christmas - the gift - giving, the Santa Claus, etc. might seem strange and unappealing to him. So, the writer of the fanfiction might have decided to make him hate it for that reason.
One common theme could be loneliness. Naruto often felt alone during his childhood, and at Christmas, this feeling might be intensified. Another theme could be sacrifice. Characters might sacrifice their own Christmas cheer for the greater good of the village. And also, the theme of unfulfilled wishes, as not all characters can have their ideal Christmas due to the harsh shinobi world they live in.
It could be that he was chasing an enemy or a valuable item that ended up in Hozukijou. Naruto is often on a mission to protect or retrieve something, and this place might be the destination of such a quest.
Maybe Naruto is short on money for some delicious ramen and thinks Kakashi might have some spare change. After all, Kakashi always seems to have some mystery about him and Naruto might assume he has some cash hidden away.
Maybe for the sake of an interesting crossover. Writers often bring different characters from various universes together to create unique and exciting stories.
Another reason could be that Tsunade is trying to use Naruto for some sort of political leverage within the village or against other villages. She may think that having Naruto in her control gives her an advantage, but as the story unfolds, she realizes the error of her ways.