Quite possibly for the same reason that many, if not most (? I've no idea, really, but certainly plenty of), SEO companies consider Google to be the only actual target, because Bing just isn't popular enough to spend the time on.
If there was a search engine out there that had 10 uniques per month would you expect people to care enough to send take-down notices to them? So where do you draw the line... for some people, you draw it between Google and Bing, not below them both.
If there was a search engine out there that had 10 uniques per month would you expect people to care enough to send take-down notices to them? So where do you draw the line... for some people, you draw it between Google and Bing, not below them both.