Answer

I don’t think they are studied less. They’re simply not continuous and not printed on the page in every topic / passage. There’s no sweeping rule about the way to study the medieval authorities (Rishonim). In every topic / passage there are different medieval authorities (Rishonim) who are central, and others who are marginal. So it doesn’t make much sense to study one particular authority straight through in order. I recommend that you choose a book that gathers the analytical topics in the passage and the commentators, and use it to see which medieval authorities (Rishonim) are central to that topic / passage and study them. For example: Beit Lechem Yehuda, Nachalat Moshe, Chiddushei Rabbi Shmuel, and the like.