Some US universities make a significant amount of money off their extra curricular programmes, especially sports. For example, Stanford Mens Football team effectively subsidises a lot of the smaller athletics programmes they have, as well as the sports scholarships the uni pays out to students. The Mens Football programme has reported making upwards of $40 million in some academic years. A lot of the players on the team will have had their full attendance at Stanford paid for, through that revenue.
https://stanforddaily.com/2017/09/06/stanford-athletics-and-the-profitability-of-amateurism/
So it makes sense that they will seek to recruit students who have suitable extracurricular interests.
Also your choice of extracurriculars demonstrates your values as much as your skills and interests. If a uni has values around being socially responsible and environmentally conscious, they're going to be interested in applicants who demonstrate that through their choice of extra curriculars, since it's quite hard to demonstrate that in your choice of study subjects. Berkeley for example is quite open in their admissions info that they value leadership, so they will be looking for demonstration of that in extracurricular activities.
Remember as well that in US universities they have to study a fairly wide range of non 'major' related topics as well as their key study area, especially in the first year or two, so having students with a broad range of interests helps to fill those classes. In my first year I had to take a health class, a science, and a physical exercise class, not related to my psychology degree at all. It also makes for a more intersting and vibrant campus life, if you have a number of interests and skills represented outside of the academic.