This is a (potentially inflammatory) subset of this question: http://meta.wordpress.stackexchange.com/questions/991/what-to-do-with-wrong-answers-marked-as-solutionWhat to do with wrong answers marked as solution?
I would follow the advice/answers from that question. Regardless of why there are so many incorrect answers to licensing questions, in the end the real problem is dilution of the correct answer - and the solution to that problem is to use the site mechanics to downvote incorrect answers, upvote correct answers, and leave comments as appropriate.