I think you make the most friends during the first year of college because you have to. You're thrown into a totally new location, no old friends or family around, you just have to make friends. Plus, many colleges really facilitate it by putting first years on the same floors, etc, having social events during orientation, etc. After that, you make less friends because everyone already HAS their friends- nobody really NEEDS to make friends anymore, and so they go about their business. I always felt like I wanted to make more friends during my upper class years at college, but it was very difficult. Especially in college, people form groups, and it's hard to befriend one member of a different group. I think it is so much the difficulty of adjusting to college life that leads to so many freshman friendships.