how do i find why in my extracurricular activity?

It depends on what your extracurriculars are, but I think one of the most helpful things that's helped me find the "why" in my extracurriculars is my interests/passions. Psychology club? I plan to pursue psychology in the future and see the importance of understanding the ways we think and interact, as well as how vital it is to provide education about mental health and self-care. Theatre club? I've been immersed in the arts all of my life and want to help make the arts accessible for all. NHS? I value the academic community that it provides, as well as the service opportunities that it has exposed me to that ultimately led to me bettering my community. Violin? I enjoy music, and find value in simply doing things for enjoyment, as well as the different cultural impacts on music.

Those are just brief summaries, but hopefully it can give you an idea of how to find your "why." Connect your extracurriculars to your passions and goals in life, and how that can impact your communities. It can be a struggle at first, but starting off with your interests can be helpful. You can also just think about why you joined the extracurricular in the first place. If that initial reason was just for college applications, maybe try to see how that extracurricular helps and impacts people beyond yourself and write about that.

Summary: find your interests/passions and connect how the extracurriculars benefit your community!

The best thing you can do is just pick one with the biggest impact for you. The one that give a unique experience to you that others don't. You can also pick one that suits your designated major as well!