Chance to trade or find tools with weapon enchantments

The only tool with this ability is the axe, which I have seen to be sold with smite and knockback on it. If trading is one of the only ways to get these special enchantments, then why can't other tools have the same ability? If all tools deal more damage than when fighting by hand, then they should be eligible for weapon enchanting, such as smite, knockback or sharpness. It would be funny to see a hoe with something like knockback, and give more melee weapon options to players if they do not choose to use axes, swords or tridents.