Plagiarism is the result of lax policies by ad companies on the web. Google Adsense is probably the biggest target and culprit. Followed by in-text providers like Vibrantmedia.com and Adbrite.com.
Websites simply steal content and reproduce it on their blogs and get paid for the traffic. Most Plagiarizing is spread out with the infringing website rarely stealing multiple times and making the hassle of the DMCA process not worth it.
We will go over the proper tactics to take if you have been infringed going forward.