Because only a few people have a truly symmetrical face. Your hair acts as a sort of frame and so a middle part can end up emphasizing the imbalances that exist and thus make you look more lopsided. There are also additional considerations to a beautiful face. Symmetry is one, proportion is the other. You can have a very symmetrical face but if your features are smaller or larger in relation to it as a whole, then that can ding off a few points on the "beauty" meter.
That's why asymmetrical hairstyles can work so much better. It can shape your face in accordance to its symmetry and proportion and thus make it appear more balanced.
So... Each instance has a copy of all the other instances' content? I thought they just had access to each other's content but not a copy?
If they each have a copy then how would refederation work? I assume they just sync back together. So if instance A has a post with several comment threads on it from other instances, and B defederates, then it gets a copy of the post. If the original author on A decides to delete their post, then their post stays on B's instance, but if B refederates, does their copy of that post repopulate or does it sync up to be deleted?