Because I love it. Because, at the risk of not sounding humble, I believe and have had confirmation in my career that I have a gift for it and to not do it would be wasting my life to a certain extent. Because I learn more about myself and the world, the more I do it. I know that allows you to go to work unshaven, still wearing sweat pants and a tee shirt. This could be an entire dissertation.
Articles are fast and and regular and teach writing discipline, economy of language, etc.
Books provide a certain status and authenticity of voice but the book industry is getting more like the film business all the time, decisions based on marketing, not content. Plays are richly rewarding for hearing the audience reaction. Expect little else. End of mini- dissertation. Just like in real life.