For a time, both Bing and Google allowed anyone to submit URLs to their search engine index anonymously, in hopes that users would help make those respective indexes better. Well, that was a dumb idea. After Google "had to drop" their public submission feature a few months ago, Bing today followed suit, citing quality and trust issues (via Search Engine Land):
(T)he URLs received are by far too low quality to be trustable, and webmasters preferring having more ownership of the URLs for their site.
Earlier this year, Bing updated its Bing Webmaster Tools to accept logins from both Google and Facebook accounts, making it easier for site owners to manage URL submissions for their own sites, allowing those URLs to be verified, which is probably what should have been happening all along.
How much difference getting rid of the spammy and untrustworthy anonymous user submitted links will make to the health of the Bing search index remains to be seen, but this is a move that makes sense. Site owners can sign up for a Bing Webmaster Tools account if they don't have one already.