Google Added A New Quality Guideline To The Discover Documentation
https://www.cnbc.comThe updated section says
To deliver a good user experience, Discover seeks to present content that’s suitable for interest-based feeds, such as articles and videos, as well as filter out content that’s not desired or that might confuse readers. For example, Discover might not recommend job applications, petitions, forms, code repositories, or satirical content without any context.