The Gemora points out Halachic distinctions betwen a Talmid Chacham and a layman regarding the issue of Ha'arama. The Magid Mishna [Shabbos 23,3] and the Beis Yosef [end of Siman 339] explain that the reason that that the Rambam does not make such Halachic distinctions is because in our times a Talmid Chacham 'can not be found'.
I don't understand why this Halacha should be any different than the laws of Korbonos, etc. which are included in the Rambam despite their lack of practical relevance in our times. Kol Tuv,
Dov Lew
The Gemara in Menachos (99b) says that certain Halachos, which are Kulos, "may not be taught in front of an Am ha'Aretz." Even though the Rambam certainly lists Halachos that are not (yet) relevant in our day, nevertheless he ought to refrain from mentioning a Kulah that is permitted only to Talmidei Chachamim and publicizing it in front of Amei ha'Aretz, who may learn from it to be lenient when it is not permitted to be.
Be well, Mordecai