Drop in Splash was to represent Briar Rabbit being thrown into the Briar Patch, so a literal drop while thrown like in the movie.
Frozen, well that is similar to TBA where they shoved an IP into an already existing attraction rather than purpose built. So it’s different. But if you want the story reason it’s because us being pushed out of Elsa’s Ice Castle and being chased by Marshmallow, similar to the movie where Elsa chased Anna out of the castle and Marshmallow chases her.
So yes from a story perspective there should be a reason story beat wise why there is a drop.
lol right first thing anyone who watched Brer Fox throwing Brer Rabbit in the Briar Patch in SotS thought was “they need to base a log flume drop ride” on this asap. It’s so obvious.