But if you consider Ravenloft to be a theme of a game and not just a location where adventuring takes place... that's when
@Minigiant 's point take hold. Ravenloft is about cursed and evil dark lords forever being tortured by dangling what they utmost want in front of them but never giving it to them. Sisyphus in gothic horror. And the entire rest of the land and people that Darklord rules over are all there merely in service of the torture the Dark Forces have put in place to tantalize the Darklord. And anything you play that doesn't have that thematic thread underpinning the adventure, the characters, and the locations could basically just be considered standard Gothic Horror. Which is fine if that's what people want to play, but it's not "Ravenloft".