Some asteroids were large enough to melt internally. The metal core started uniform and homogeneous. But, as temperature dropped, the alloy very gradually stabilized. Because cooling happened to occur over millions of years, atoms had enormous amounts of time to separate and settle into the most ideal, low-energy distributions and configurations (i.e., octahedral geometry). On a planar cut of meteorite, the "Thomson-Widmanstätten pattern" is what post-homogenous, melted-metallic symmetry looks like when in it is allowed to cool for millions of years, and therefore cannot be replicated in a lab. Philosophical parallel:  Internal commitment transcends what is on the surface and is not confined to the short term.