But literally every one of these items has money attached to it. This is a game, and the things that are coming back have nothing to do with money and everything to do with time commitment, and the time you were playing wow.
Most people don’t look at transmog/pets/etc and be like “oh I’d love that because it’s hard to get” most people are just like “hey they looks cool I want to get that”. If you want to have things to boast about how hard they were to get, there are achievments for that are literally designed for that.
I’m not saying every cosmetic/reward should be made available (for example PvP rating sets and AOTC achievement rewards should stay as only obtainable during those times) but other than that there’s not really a reason to timegate them other than “I have it and you don’t so bad luck”. Just let people collect things while fun things in a game they like.