The Rambam was looking forward to the future when we would no longer be in exile and living in Eretz Israel, (may it be soon and in our day) and we would no longer need the local minhagim of our Hakhamim and bet din to keep us unified in the exile as a family unit (Klal Israel), but as a nation gathered together, with Shoftim as in the days of old. Bound by the minhagim of Eretz Israel and the great Sanhedrin.

This is the reason the Rambam did not focus on customs in his approach to his Halachah and writings.   The Rambam was both living in the future and anticipating our Kibbutz Galiot.