Because it establishes you as an authority on the subject that you are writing on and because writing articles will also increase the number of people (and visitors) who know about and visit your website.
Writing articles and allowing other webmasters to post your articles on their website will absolutely explode the number of backlinks to your site, in addition to increasing the number of people who visit your site ? both of which help to increase your website's popularity and search engine ranking.
The best part about giving away free articles for other webmasters to publish on their own website is that this sort of thing is viral ? so you could end up getting thousands of visitors to your site from just one article that you wrote.
Think about that for a moment.
You write an article and then make it available to webmasters to post on their site, because they need content for their website. But on every article that you write, you have a link back to your website ? so in a way they are promoting your website in exchange for you allowing them to post their article on their site.
So, if your article gets published by twenty webmasters, you will automatically have twenty additional backlinks to your website, along with twenty additional streams of traffic coming to your website.
Also, the visitors who visit the webmaster's site and see your article automatically make the assumption that the webmaster endorses you and your website. That makes these visitors a little more likely to visit your site than if a link to your website was just listed on their links page.
With advantages like these, you can see why you want to submit your article to as many different websites, forums and article directories as possible.
