1) Write to get it out of your head? Instead of therapy, it works. 2) Write to see if others share your opinions? Sometimes they do, sometimes not. 3) To make money. If you have the connections, advertising will come, even with low audience. Look, my readers are top 100 CEOs. How many have time to read? A few. Ads for Porsche will come. 4) To get work. A good blog will draw job offers or will convince your interviewer to hire you. And probably other reasons.