Gary Illyes from Google said on LinkedIn the other day that sitemaps are hints, not orders. Meaning just because you submit an XML sitemap file to Google, it does not mean Google will index and rank that content.
This is not a new statement, more of a PSA, a reminder that Google does not have guaranteed crawling, indexing, or ranking of your URLs.
Gary explained, "A sitemap file, as defined by sitemaps.org, is a great way to tell search engines about your site's URLs. But that's where it ends: you tell Steve to read your sitemap, but if Steve doesn't trust your site will delight users, it won't bother reading your sitemap."
Steve is Gary's hypothetical search engine, if you were wondering.
Forum discussion at LinkedIn.