Because thats how purists thinks, they dont care about content of change and if it good for game or not. For them is game perfect and they are stubborn so they refuse any kind of balance because its “change”.
I am pretty sure they changed recipe many times. But you talk about one specific product which is far from complexity of diablo 2. You cant compare it like that. But even if you would, lets say some people. Will be disgusted by colour of Coca Cola so they will decide to change recipe and add multiple different colour variants. Taste will be exactly same as current version. Purist will refuse other colour variants even when they dont have different taste.
Inovating is they way humanity is going forward, staying the same will not get you anywhere.