We need to be very careful when defining are terms. Calling things that aren’t really a Mitzvah a “Mitzvah” can lead to serious problems. People should get into the habit of using precise terms. Once again, what it the “Mitzvah” of following the Shulchan Aruch?
And the Gemara (Brachos 8b I think) says that someone who does Shnayim Mikra gets long life. From there the Shulchan Aruch realizes it’s a good thing and brings down to do it. So we have to understand exactly what type of obligation that entails. Just shrugging everything off as a “Mitzvah” does not do justice to any Halachos, whether they are D’Orasia, D’Rabannan, Minhag, Hanhaga, or an Eitza Tova.