If you'd actually read the rules (which were drawn up by a few members, including myself, and some forum moderators) thoroughly you'd have noticed that far from saying that we wont explain it - they simply ask people to keep discussion like this to PMs. They're not up to negotiation, as they've worked fine for a long time now, but I'm sure most of he thread regulars would be happy to clarify stuff in private. The reason we don't like to talk about it in here is because threads get clogged up with off topic arguments started by people such as yourself, and that didn't help anyone...
Otherwise, I think RLF's answer was firly clear. "Hair metal", like "nu-metal", was a title given to bands with a particular aesthetic by record labels, radio stations and music journalists which has little (musically) to do with the metal genre as it is widely understood today. Yes, genres aren't static predefined things, but nevertheless the wide variety of bands that cover what is most commonly understood to be "metal" do share a lot musically and in terms of fanbase that nu-metal and hair metal (and metalcore) don't.