First of all, you may not enjoy writing the articles yourself, or may just feel that you don't do a good job of it. Secondly, many online business owners simply do not have the time to write all of the content needed to draw traffic and help increase rank with the search engines, so they hire a ghostwriter to do the work for them.
An exceptional article ghostwriter can write articles that are not only well-optimized for your keywords and phrases, but are interesting to the reader which is important if you want them to continue reading down to your author resource box, so that they will click through to your site.
Personally, I have hundreds of articles on Ezine Articles and have an average click-through rate of 25%. Some categories I have written in get click-through rates of 40 to 50%, which is unusually high.
If you want original content that attracts targeted traffic AND search engines, consider ghostwriting services - but do your research to make sure you're getting what you pay for! There's no sense in paying someone good money to write for you, then having to re-write it yourself because of poor quality work.