Since stranger things been back why hasnt nancy, steve and demo got their achievements back

I've actually seen the answer to this. Some platforms can be sticklers about changing achievements unless they're physically impossible to do anymore, so they haven't changed them back. I don't think this is entirely the best reason to go with since they can just simply… add them back as new achievements? However, that's the reasoning they seem to have gone with so that's what we're gonna get unless we complain a lot.