I’m merely relating what I was told by AOs. @JanieWalker
When I was going through the admissions process a couple of years ago, I went to an Exploring College Options event, which had reps from Harvard, Stanford, Penn, Duke, and Georgetown, among others. During the Q&A, someone asked, “What do you think of applicants who self-study for additional AP’s over and above the AP classes they take?” One rep responded, “Please don’t do that. We’re not impressed by that.” The other reps all nodded.
As to why, I’m guessing, but here are my thoughts: Nothing says one-dimensional more than listing self studying APs on the app. Colleges want applicants to maximize their academic experiences in the classroom, and to use their time outside the classroom for something other than academics. Additionally, I’m not sure that performing well on a 3 hour exam is necessarily indicative that one “is ready for college level material.” I’ve told the story before that I did not take a psych class in HS, and my only prep for the AP Psych exam was reading through Barron’s the weekend before and I still got a 5. Clearly not doable for something like Calc BC, but goes to show that not all AP courses/exams are considered equal, IMO.