Having a Difficulty everyone plays allows the community to share their experiences without having to put a Caveat on them e.g. “just beat Elden Beast, that fight should have let us use Torrent but I got it done I feel so happy” then other players who beat the Final Boss who faced the same challenge can relate to the experience. If there was a difficulty option then every time someone beat a Boss or dungeon and talked about it the community would instantly respond “what difficulty where you on?”, you see this with summons and OP weapons already.

So the answer is having no difficulty option actually reduces gatekeeping.