Because they're chemically identical, much in the way methane, kerosene, and wax are chemically identical to each other. The different substances have very dis

Because they're chemically identical, much in the way methane, kerosene, and wax are chemically identical to each other. The different substances have very dissimilar properties but they behave themselves next to each other without making chemical reactions. When you get down to microscale, little annoyances in the big world end up becoming dealbreakers, like different coefficients of thermal expansion, and potentials and bandgaps that show up between different elements and compounds, particularly as chemical reactions between them take place.