In 20w12a, MC-174467 was fixed to allow soul sand to support soul fire. However, the crafting recipe for soul fire torches still only allows soul soil to be used, and not soul sand.
In previous snapshots, I would have said this was WAI. However, after the change this snapshot, excluding soul sand from the recipe is an inconsistency and should be fixed.
That's just how the game is. The crafting recipe requires soul soil not soul sand.