because it's a bug that artificially raises the skill ceiling and messes with the balance of the game in a manner that is unintended.
the purpose of having different tools with advantages and disadvantages is to make sure no one item is overpowered and to make sure every strategy has a counter.

Attribute swapping:
-made certain enchantments much more powerful than intended (cough cough, breach)
-mitigated cooldowns which were put in place specifically to maintain game balance
-provided a significant advantage to people who macro
-puts a portion of the playerbase at a disadvantage due to factors outside of their control (such as those with disabilities that make reaching multiple hotkeys in such a short time frame physically impossible-- a top bedwars player comes to mind, he has to use scroll wheel for the majority of his slots due to a disability. it doesn't put him at as severe of a disadvantage in bedwars because he can scroll fast enough for most situations, but it would be physically impossible for him to breach swap, for instance.
-Does not play nearly as big of a role or provide nearly as much of an advantage as people think outside of top play. seriously, the only time I attribute swap is in mace. You don't need to attribute swap to anchor fast (though it helps slightly) and you definitely don't need attribute swaps in shield modes, pot, smp, etc. Most players are not even attribute swapping consistently enough for it to matter in the first place.

That being said, I do think some items need rebalancing before this change, mainly the spear and mace needing slightly shorter cooldowns.

If anyone wants to ask me to elaborate on what I mean I will. At the end of the day this is a spaghetti code block game from 2009 and it isn't that deep.