Google Won't Use Your Sitemap File If Its Not Convinced Of New/Important Content
Google may ignore sitemap entries when it believes the site lacks new, important content or when crawling limitations exist; sitemaps do not guarantee indexing.
Bing Webmaster Tools Sitemaps Index Coverage Missing
Some sitemaps in Bing Webmaster Tools show missing Index Coverage buttons, possibly due to insufficient data for those sitemap files; Microsoft has not responded.