Because he, like a lot of young people, had a limited amount of job experience back then and included college activities.
I included college activities/memberships in my earlier job applications, which I did not include on later applications when I had more job experience.
I just remembered that on my initial job application out of college I included that I was the leader of a group called the "Reformed University Movement". It was a group we formed so that we could sign up for a room on campus which we used for our church to meet on Sundays.
So far as I know, we never had a meeting, we had no budget, no members, and I had completely forgotten the whole thing until I was reviewing my resume.
BTW, which life insurance company did Mary Jo Kopechne pay premiums to, before she was killed?