Ask HN: What is the purpose of social media?

I am a lifelong technologist. I have started or joined a number of reasonably successful projects and companies in my time. I've had some good exits, and I've had a lot of fun. I'm generally very passionate about what I do, and I love seeing the accelerating advancement of technology.

However, I am an absolute noob when it comes to social media. I set up a twitter account roughly three months ago, and I have been tweeting regularly since. After various articles convinced me that starting a blog would be an interesting experiment, I established a tumblr account and wrote my first blog entry, literally today.

That said, I really don't see the point. My experience with twitter has led me to the inevitable conclusion that nobody cares what one has to say on social media platforms -- and I don't understand the value of communicating into a vacuum.

So, I come to you, HN. What benefit is there of participating in social media? What am I missing? Thanks.