Since all posts published from WordPress now have the x-robots-tag “noindex” header, it’s also important to remove the URLs from the sitemap.xml.
When a URL is marked with a noindex tag, Google crawls it less frequently, to save crawl budget. URLs included in sitemaps.xml are supposedly important, and so, are prioritized for crawls. So the message passed to the crawler is confusing.
The internet is too big and Google is always trying to prioritize in order to save resources. Some SEOs even believe that this can lead to PR dilution.