Traditionally, there are seven rabbinic commandments to be added to the 613 in the Torah: Hallel, Purim, Hanukkah, Eruv, washing hands, lighting Shabbat candles, and saying blessings.
But there are many other requirements decreed by the rabbis over the centuries and found in Mishnah, Talmud, Mishneh Torah, Shulkhan Arukh, etc. Why are they not also considered commandments? Perhaps because they derive logically from the 613? Or because they are not deemed as important (and if so, why?)?