No sitemap is declared
The file contains no "Sitemap:" line.
Consequence. Crawlers have to discover every URL by following links. Pages that are deep, newly published, or poorly linked internally take longer to be found, and some may never be. A sitemap is the most direct way to hand a crawler the full list.
If that is not intended. Publish an XML sitemap and declare it with an absolute URL, e.g. "Sitemap: https://example.com/sitemap.xml". The line is global — it belongs outside any User-agent group and applies to every crawler.