Why isn't this page linked in the sidebar instead of in an article's appendix?
This is a test of the template and the page. There is no sidebar on the mobile website, and more than half of readers at popular articles are using the mobile website. Even among users of the desktop site, there is no evidence that non-editors look at the sidebar. Also, the contents of the sidebar appear in all articles, which means that small-scale testing cannot be done through the sidebar.
For the average experienced Wikipedian, yes. But the Education, Libraries and GLAM outreach community have long noticed that these very simple assumptions about how Wikipedia works (like understanding WP:Verifiability or how our anti-vandalism works), are missing from a wide variety of readers. Research by librarians and educators supports this conclusion, and in WMF consultations with readers, we still get major questions and concerns about Wikipedia's credibility and reliability. For most of our readers, they need to be reminded of these details to successfully use our projects in basic research, and to learn to contribute as editors.
