Harvard and similar schools have moved beyond just being smart. Everyone who applies is super smart. Now the yard stick is smart++ (meaning they want you to be "well rounded" which is code for having a bunch of self-driven/extra curriculars/special skills/x-factor etc to make you a stand out).
And yes, schools in the US do care, deeply, about extracurriculars. Harvard could fill every seat, every year, with the valedictorian of a different high school class. Since nearly every data point is tightly grouped on the most immediately available metric, they turn to other data points to make their decisions. (And there's a long history of using that flexibility for both exclusionary and inclusionary purposes.)
Harvard ran out of other measures. When all of the applicants are capping out every academic measure, you have to start to look beyond.
On all these metrics I would be seriously surprised if they have many more amazing applicants than places. If that is in fact the case, they should make more places available. It almost never happens that you get someone that is 10/10/10 on all metrics.