might be a thing where existing releases of the game are grandfathered in somehow to still be sellable. or maybe the jackson estate just doesn't even know about those and the second someone tells them they will vanish forever, in which case sshh
SEGA eventually stopped releasing the original roms on new hardware; they never released the roms on PSN. So it sounds like they got scared. It's strange they didn't take the roms down from other platforms (Steam, Xbox etc).