In Va-eira when it mentions Moshe and Aaron's lineage (Shemot 6:14) it also lists generational details about Ruben and Shimon. Why are Ruben's and Shimon's lineages listed here?
Rashi asks this question, and answers it in 2 ways:
רש"י: אלה ראשי בית אבותם. מתוך שהוזקק ליחס שבטו של לוי עד משה ואהרן בשביל משה ואהרן, התחיל ליחסם דרך תולדותם (ה) מראובן. (ובפסיקתא גדולה ראיתי, לפי שקנטרם יעקב אבינו לשלשה שבטים הללו בשעת מותו, חזר הכתוב ויחסם כאן לבדם, לומר שחשובים הם):
שפתי חכמים (ה) וא"ת עדיין יש להקשות למה לא התחיל משבט לוי. ותירץ הרמב"ן דא"כ היה נראה שלוי הוא בכור היחס מכאן ואילך לכבוד משה לכך התחיל מראובן להודיע שנשאר ראובן בכור ליחס ונמנה לוי שלישי לשבטים:
In his first answer, with elaboration from the Sifsei Chachamim based on the Ramban, the reason is so that it shouldn't be assumed that the tribe of Levi has now gotten some first born status.
So the Torah begins in the correct order of genealogy until it gets to the point it wants to make. No point in continuing with the other 9 tribes, as global genealogy is not the issue at hand.
In his second answer, based on The Psikta, he says that it's to reinforce that these 3 tribes are in integral part of Bnei Yisrael, despite having been condemned by Yaakov when he blessed the [other] tribes.
The Meshech Chochma to that verse writes that Hashem went to great lengths to make it clear that the Jewish people were not mindless followers of Moshe and Aharon. Therefore, the Torah identifies that there were a series of detractors who questioned Moshe at every step of the way. The Torah mentions right here, at the beginning of the confrontation with Paroh, those who particularly challenged Moshe, namely from Reuvein the house of פלוא (Dasan and Aviram), from Shimon the house of שאול בן הכנענית (Zimri), and from Levi, Korach.
Additionally, the Meshech Chochma explains that this is why the Torah (Shemos 7:7) concludes with Moshe and Aharon's ages before getting back to the encounter with Paroh, to point out that they were old men and would not have had the zeal to fool an entire nation and lead them into the desert if not that they were commanded by G-d to do so.