Hanukkah is one of the two major rabbinic holidays, the other being Purim. Some people like to therefore classify it as a “minor holiday” in Judaism, but in reality the distinction only comes whether it was dictated to Moses, which given that the events happened over a thousand years after his death is simply not possible. However, what does make it stand out is that while the other major rabbinic holiday of Purim gets its own book in the Written Torah (Megilat Esther), and it’s own tractate of the Talmud (Mesechet Megila) the events and laws concerning Hanukkah have neither.
Why not in the Written Torah?
The Written Torah, also known as the Tanakh, has a particular end. Although not ordered chronologically, the last events detailed are a relatively short time—around one or two generations—after the construction of the Second Temple. The reasons why it concluded with the writings of Ezra haSofer, who wrote the Book of Ezra, the Book of Malachi, and Divrei Hayamim (“Chronicles”) are beyond the scope here, but that is what happened, occuring before the Greek conquest of the Persian Empire and with it the Land of Israel.
In the Apocrypha
There are texts, called 1 Maccabees and 2 Maccabees, that detail the events, and give some theological understanding, but these are not considered part of the Torah in any way. First of all, it is not divinely inspired and appears to be written by a Roman court historian. Also, the two books contradict each other in tone and understanding of the events. Maccabees details history of battles and treaties far more than it might be considered really a religious text. Perhaps it is interesting as a historical document, but it is not divine. The reason for this may also be related to its lack of prominence in the Oral Torah.
No Book of Talmud
The matter that Hanukkah has no tractate of its own in the Talmud can be somewhat overstated, but it is still true. The titles do not limit the scope of material; consider that the laws and other matters around Purim are contained in Mesechet Megila, but already after the first page it has a detour to talk about the history of biblical translation and the Hebrew alphabet in depth for instance. The vast majority of the laws of Hanukkah are contained in Mesechet Shabbat. This is unlike the Written Torah without any mention of Hanukkah or the Maccabees whatsoever.
One answer as to why it does not get prominence on its own is that the story of Hanukkah is about fighting back the Greek influence, but it simultaneously involved a civil war. The Torah, especially notable in the Oral Torah, is enormously concerned with unity among Jews, and so highlighting a time when assimilated Jews warred against religious Jews, is not something that shoudl be focused on excessively, even though the religious Jews won the battles.
The Result
While it’s very fashionable these days to drudge up the “real” or “dark side of” history, and so many Jewish outlets have been publishing more about the civil war element in recent years, the mainstream understanding is that of a war of independence to allow the Jews to practice the Torah. Ultimately that is true, even though many Jews tragically did not want to see themselves as Jews, and rather as enlightened Greeks. The reality of civil war—which also becomes overblown as there was certainly harsh foreign oppression—is not as important as the symbols of increasing light, reclaiming the Temple for its proper use, liberating the Land of Israel, and uniting the Jews, newly independent. It is not that Hannukah was forgotten for lack of notariety in the Torah, but its worst elements perhaps were.
