It's just a bonus

It would be pretty overpowered, because this datapack and alikes allow you to pratically transfer enchantments from otherwise useless items into end-game ones; and obsfuscates the whole point of enchanting a item. Take a gold pickaxe, for example: gold tools are generally useless because of their low durability, but in spite of that, they have the highest enchantment weights (that is, it's more likely you'll get Fortune II on a gold pickaxe than on a diamond one, for the same enchantment level). So you can just make a gold tool, enchant it, upgrate to diamond, merge it with another tool on the anvil, and you'll quickly max all enchantments. Not to mention you can do this with all the enchanted trash you find on loot chests (like those with Mending and treasure enchantments).



Mojang's way of "balancing" this was to introduce the grindstone and let you remove enchantments for XP; but they give proportionally way less XP than simply mining quartz, for example - and pathetically less than an enderman end XP farm. So...yeah...this is why there's so many enchantment merger / disenchanter datapacks out there.