It has to do with the severe decrease in value and trust that Google once gave article sites like ezinearticles.com. Once beloved, Google chose to recalibrate their level of importance. Once this occurred, the value of the content, links, and everything related to such sites plummeted.
While I do not want to go as far as calling them a graveyard, in which if a link of yours is found in them you get demoted, it was and is extremely close.
Links from quality sites are still vital, however the strategy has changed. This should be a lesson to anyone who puts their eggs in one basket, doesn't diversify their link building, or treads in areas that may one day be considered suspect by the big search engines.