Fasting on the 7th of Adar

Regarding fasting on the 7th of Adar, The Shulchan Aruch (580:2) designates the 7th of Adar as a day of fasting in remembrance of Moshe Rabbeinu's Yahrzeit. Elya Rabbah (580:1) says one who fasts on this day is assured a place in the world to come. The Tur (580:1) cites the Bahag that it's even a biblical obligation to fast. The Bais Yosef (ibid) clarifies the intention of the Bahag that even though the rabbis established this important day, it should be approached with the same reverence as a biblical fast day. Perhaps we don't find people who fast on this day based on the Bais Yosef, who says, "I never saw or heard of anyone who fasts on this day."