For me, the difference is that very few people and even fewer small children would have been excited to go on a Song of the South ride because they loved the film. The ride was always promoted more on the basis of the 'splash' or drop rather than as a ride through the world of Song of the South and, indeed, the IP was chosen because it suited the ride system rather than the other way around. So, I think most people deciding as to whether they were going to go on the ride were deciding based on whether they wanted to brave the thrill aspect rather than on the basis of the characters.
I would imagine Princess and the Frog is different because it is a film that particularly children will likely have a connection and the IP will be a draw in and of itself. For similar reasons, I suspect if there is a thrill element to any Moana ride they eventually build that it will be relatively mild.