I think it might be as simple as we don’t encourage it in the apps. Look at how warpcast works. Simply putting it there in the post UI does a lot to change how people post. At the moment groups / channels / communities are a kind neglected part of Nostr. https://image.nostr.build/b409fa439133fc19822cb8381becb15b5d4e6dfa2a574118dc70170de821b37b.jpg https://image.nostr.build/e7a1da793fabb501da3272647879824669fbb44cd7105758fb456ab43f573c3d.jpg
Manual classification of notes in this way has great potential, but it also opens the door to easy spam/crosspost, such as tags. I believe that the user should join a specific channel before posting. Groups are a good example of this flow, but notes are segregated and so they lost visibility. Difficult matter. I agree that this is an area where we should put more effort.