It is the only one where the possibility of a more "generic" land exists with different IP capable of being swapped in and out, which is generally more consistent with how the other lands of Magic Kingdom are. All other concepts floating around in the ether at the moment would be facsimiles of locales from their source films with very little wiggle room as the park evolves. They'd ultimately have to be leveled or lazily papered over in some way if the IP ever falls out of favor, whereas villains would be a perpetual thing that they could renew.