Note that the Alter Rebbe does not mention this custom in his Siddur. (There are, of course, additional matters that the Alter Rebbe omits from his Siddur, despite the fact that they are indeed our custom.) However, even when this custom was [subsequently] added to Siddur Torah Or and Tehillat HaShem, it was merely appended to the end of the Siddur, following all the other prayers. Further, it was merely mentioned in a footnote to the Torah reading for Chanukah (for that reading was likewise belatedly appended to the Siddur), which is also followed by the Yehi ratzon prayer recited after the [daily] Nasi.
aCALLtoACTIONThis, perhaps, is the reason for the unfortunate neglect of the custom to recite the Nasi, and even greater neglect of the Yehi ratzon (which, although mentioned in works of foremost Torah authorities is not mentioned in the Shulchan Aruch’s discussion on reciting the Nasi …).
It is a mitzvah to bolster this custom (Parshas Tazria 5749, fn. 76; Hisvaaduyos, p. 530).
Reminders are essential
On Chanukah, these same portions are read to the congregation from the Torah and therefore do not require further promoting. Conversely, during Nissan, each person reads the Nasi to themselves, which is why we need to actively promote and remind everyone to recite it.
The essential point is that through [promoting and observing] this custom, we hasten the dedication of the Third Beis HaMikdash (ibid., p. 534).
A Jewish custom is precious
It is a mitzvah to bolster this custom, and to do so in a manner befitting the activity [of carrying out a custom] described [by G-d] as “the practices instituted by the Sages [that] are more important and cherished to Me [than My own commandments!” i.e., as befits the preciousness of a custom established by Jewry. (In this regard, reciting the Nasi may be compared to the custom of Hakafos on Simchas Torah) (ibid., fn. 76; p. 530).
