the enchanter costs levels to enchant, however when you remove the levels from the player, you are doing exactly that. the problem is each level increases the XP required to reach the next level. this is a problem because if hypothetically someone at level 10 spends 4 levels to add an enchantment, then it would cost them 40 experience. however, if someone at level 68 did the same enchant that costs 4 levels, they would lose 1726 experience. from what I understand Minecraft stores a player's xp in a 32-bit integer and the cost of an enchant can be calculated with the equation: (2*L)+7 Where "L" is the level cost of the enchantment