Four reasons in fact. Here's an excerpt from the first reason, validate your expertise:

Someone once said to me that most of the value created in the new economy is through writing. I’m not sure that I entirely believe this but I believe the sentiment that in a knowledge-based business the outcomes of writing are product and value.

— Four Reasons to Write by Win Without Pitching

I've quietly relaunched my software development blog and plan on writing a couple of articles a month. I'm doing it not only because I like writing but to also test my knowledge and experience with my others in the software development industry.