You really asked a very important question. But to you, it is not important why others started Aikido (there may be a wide variety of reasons), it's only important why YOU started. It's not important what this reason is, it's if it is good enough to keep you going.
But I'll tell you why I started Aikido, maybe it helps you to realize your own reasons. After I stopped dancing I wanted to go on with sports and do something useful, so I started Tae Kwon Do, but it seemed to aggressive to me. I then tried Aikido at the University club, because it fitted nicely in my timetable. I have a really good teacher and got fascinated by his movements and understanding of the ways you can use your body. I also saw the progress of all the other students. But at the moment, I know, this is silly, I just want to get rid of my brown belt!!!!
I hope this will help you a little,