The argument for these being craftable might be valid if you could change perks on the fly. But since you have to go back to the Relic every time you want to change them around it would just add to the tedium. Of course, you could make multiple different copies with different perks, but then you're right back to the same issue with the RNG versions. Crafting was a way to get the perfect rolls on a weapon, not every possible combination. It's a great system when each weapon only has maybe 2-3 god roll perk combos, not dozens of "collectible" perk combos.