Because they take more work then they are worth.
I have tried several article spinners and the results for everyone of them ranged from poor to terrible. Even the article spinning software I purchased was not much better then the free article spinning software.
The idea that you could cut a corner and get an article that was unique and helpful from spinning an existing article does not work online today anyway. With their many updates in the past Google has told us they are trying clean up the Internet and get rid of duplicate content.
All an article spinner does is replace words with similar words. If you leave it up to the software you will have an article that reads poorly and one you have to spend time making corrections anyway.
Do yourself and your readers a favor and use one of three strategies.
1. Hire a good freelance writer. I understand this will cost you a little bit up front, but the payback is worth it.
I can write you 400 word articles for $12, and 1000 word articles for $30. Buy one and let me publish it for you and then you spend all week promoting your new post. This is much better then adding 100 articles that are already on someone else's blog.
2. Use a content mill. I do not like these because you have little input on the finished article. They are a little better then article spinning, but not much.
Plus you almost always end up getting your article written by a non native American speaking writer. I know this from personal experience on past blogs of my own.
3. Use Dragon Naturally Speaking. Just write like you speak with this voice recognition software.
This is what I do everyday. I am no good at typing and found I was spending more time correcting typing errors then writing new words.
This got stressful as the day wore on. Not so anymore.
Now I dictate all of the articles I write. I get more done and it takes very little time to proofread and make corrections.
You can do this for your own blogs as well unless you are just too busy. If that is the case then hire me and let me take writing fresh content off of your workload!
I am way better then every article spinning text rewriting content creation tool on the market! :-)
Related Article: Does Article Spinning Still Work? Or Is It Just a Waste of Effort?