Why are you advocating for taking keys offline just because of who’s hand it went through when they were bought perfectly legally?
Buying keys on Steam to resell them is directly against their policy specifically so that developers feel comfortable putting products on sale. If a key was purchased by a reseller from Steam then they can legally use it, however they can't resell it. Many do. They're the one doing something wrong and fucking people over, in order to insert themselves as an unofficial middle man and leech money.