in the 80s he didnt categorically deny every rumour going around. In the 90s he didnt do this either, why change the habit of a life time? He knows its not true, so should we? so whats the problem
He said it himself, you hear a lie often enough, you start to believe it...why would him hiring someone to say this isnt true do anything to combat it, they'll just make up another one, thats their job. Furthermore, him addressing it just brings more heat to the lie, people wonder "why is this a big deal to a popstar like Michael?" and then the press get their own way because they have ruffled Michaels feathers so to speak, they have brought him out of silence to think about what they have written.