I don't see why this is bad - groups shouldn't necessarily reach out to as broad an audience as possible. Like a sales funnel, the advertising in the group works better when it serves to filter out people who are incompatible with the group.
Your mindset reminds me of the ask/guess culture post on metafilter, which is a framework where people typically adopt either an attitude of explicitly asking for social expectations vs intuiting them through social context. You seem to prefer the latter, where people are expected to understand the implicit boundaries of the group through personal observation. There's nothing wrong with that; it doesn't mean the other way is inherently wrong, though.