How exactly would getting the materials for free make the tradecraft leves more challenging?

Let me share something with you: You get a +200% XP bonus for turning in an HQ item to a tradecraft leve. Plus you get a roughly +200% to +300% XP bonus for each item you attempt to make HQ. If you're just buying finished items off the vendor to turn in, you're seriously wasting your money and throwing away tens of thousands of free XP.

THIS is why you don't get the materials for free. You can go get a freaking pickaxe and hatchet, maybe spend an hour gathering, and have literally everything you need to make a huge batch of items for a tradecraft leve that will yield, all totaled, at least six times as much XP between the HQ crafting XP bonuses and the HQ turn-in XP bonus.