I don't know why he went there. Surely not because he didn't want his AIDS known because didn't he come out and tell us all just before he died?
Rock Hudson went to Paris because Luc Montagnier had figured out the virus before the American who later claimed credit for discovering the virus that Luc Montagnier eventually successfully sued.
Long winded way to say Luc Montagnier was the cutting edge in battling the disease and Hudson had the money to go there. And, you're right, he did come out before he died, to bring attention to the need to make every effort to stop the disease from killing millions more people.