The materials that come from monsters have always been in a weird place. The drop rates for all of them are really bad, and the retainer ventures to get them only give you 10, yet the recipes requiring them want just as many of them as equivalent crafts with mining and botany materials. To compound this, monsters in the overworld give almost no exp and aren't really worth fighting, so there isn't much of a cushion of these items available on the market from people out grinding exp like you would see in other games.