That's a nice question. It would really bring out the brain out of me. I don't really know the answer.
Honestly, my purpose why I blog is that I can shout out what's on my mind. Blogging is like writing down my diary. Before, I love pieces of papers and then I would write down my thoughts on that paper. Sooner, I've realized I got so many notes on the wall and up to the ceiling for my crazy habit. I also love writing my friends too but I don't get to mail it to them. At my desk, in the office, I have a lot of post it on my table, on my LCD monitor and everywhere else.
One day, one person introduced me to blogging. I said, "When did this come out?" "Am I really that homo sapient that I don't know that there came blogging?"
Literally, I was a little shocked but I got to keep poise and pretend I know something. Really, I DON'T KNOW A THING! Here I am, love to do a blog. Most of the time, when I don't have anything else to do, I do blogging.
For me, the answer to that question is that blogging is a habit. It is a habit on writing down a shout out wherein other people would read and know what's on your mind even if they don't know you personally. Blogging is a part of someone's life, wherein letting out of what's on that person's mind is some vitamin to others who get attracted to it or addicted to it. It is a life to others whose love of flowers, of cars, of landscapes, or of anything that is dear to them like family, friends, lovers. It is actually anything you want to share or anything you want others to know. That's blogging. It's not a fad for me maybe for others.
I hope you would start your blog soon. You can link your blog with mine.