There is no one answer to the question of why do we write. Some do it to express themselves, others to make a statement, some for money, still others for fun.
I can tell you why I write, though. I want to emulate those writers who express feelings and thoughts I didn't know I had until I saw them in print. The idea that someone, upon reading something of mine, will put down the page, or raise their eyes from the screen, and think "That's so true! I hadn't realized it until now!"
Is this conceit? Maybe...
I remember when I was very young, back in the glorious seventies. We were immortal, we were destined to become great..., great what? I don´t know. But our names would be written down somewhere. We were going to do wonderful things. I was going to sing and become famous. Now that is conceit. Having a good voice was certainly not enough.
Can something written in my blog cause someone to have an epiphany? Only time and some more work on my part will tell.