Many people choose to have a random roommate because they are worried that if they room with someone they are close friends with that it might ruin their friendship. Living with someone is entirely different than being best friends with someone, you have to be around this person all the time, share the space equally, understand each others schedules, and most importantly show respect.
College freshmen tend to be more difficult to live with because they still aren't sure who they really are or what they want out of life. Young students are constantly re-evaluating their morals and finding out what is true to them. A lot of my friends have changed, some are more aggressive, others are now in relationships, and many have joined sororities and fraternities. I am sure that I have changed a lot too.
Have you had roommates or close friends that have changed since freshman year?