When a badlands generates in large flat areas at relatively high elevations, red sand barely generates, or not generates at all on terrain because the biome thinks it's a plateau, when technically it isn't. However you can still find badlands on lower altitudes with fair amount of red sand.

Before the new terrain gen badlands often generated valleys and plateaus, where in lower areas sand would generate (with terracota below), while hills and plateaus would have mostly terracota. But now that's no longer the case due to biomes no depening on terrain shape, so the side-effect is making this material harder to find in these flat high areas.

As said before, sand still generates in a lower heights (y<80), but only on edges if the terrain is low enough, which makes badlands on different locations slightly inconsistent.

Expected result

Red sand being able generate higher (at least a bit) in those flat areas, due to the new terrain generation.