I’m a mod in one of the big FB keto groups, and admittedly I do understand some of your concerns. I can only address your questions from my perspective for what it’s worth (hope it helps).
In our group, the pinned post is very carefully curated for the info it contains. In fact, I’m pleased to say that it’s less “rules” and more FAQ. Our admin team has spent hundreds of hours over the last several years refining it. It’s not very long, is well-organized, and contains the answers to newbie FAQs that we see again and again. In short, it’s a very valuable link. When our team or a member refers newcomers to it, it’s for several reasons: one, to ensure that everyone gets consistent info to start, two a newb can read it and digest at his or her own pace, three the newb know where to find it in the future when s/he wants it again, and finally it cuts down on the potential for snotty answers from impatient members who get tired of seeing the same 10 questions over and over. As someone said below, out of the 100K+ members in our group only a certain amount are active, and believe me, though most are patient, there are only so many times you can stand answering the “How do I start” question, hence, the carefully curated pinned post. You can guess that we want to help all members from the person who showed up because they “heard about it from a friend,” to the T2 diabetic whose doctor told them to do it, to the person who has been eating this way for years and is looking for support on fasting. As volunteer admins, we spend hundreds of hours of our personal time per week doing admissions, redirecting rude posts, providing vetted articles and resources, taking down spam, sharing new research and podcast episodes, comforting sick folks, and helping troubleshoot for those who are not meeting their wellness goals. Under those circumstances, that pinned post is a godsend! I hope this helps at least resolve some of your questions in a way that shows the other side of running a group of that magnitude.