what client adds "pubkey","npub" and "created_at" in their user's kind-0 content object and most importantly, why??

kind-0 is user information, it is not a place to simply put stuff to simplify your client UI. those fields can already be derived, no need to add them again just so your client can display it more easily... clients need to be smart, not dumb, and more importantly, they need to think that other clients exist and do things differently. don't push your client architecture onto the user's content, that's not a good thing