Metals have what’re called delocalized electrons, where electrons just kind of wander around a metallic bond between atoms. Metallic bonds involve a very low level of attraction between the nucleus and its electron cloud. Turns out most elements have this, so they do metallic bonding.

It’s only when atoms start to get a little wobbly do they exhibit enough electronegativity to perform ionic or covalent bonding, where the molecules donate electrons. Electronegativity increases on the right side of the periodic table when electron valency starts getting lower. And that’s the non-metal side.

So the answer is basically that you need more of an electrical charge to exhibit the things we’ve classified as non-metals. Metals are more chill and generally less reactive.

I should also mention that non-metals have a liquid/solid metallic phase at certain temperatures and pressures. I remember a Chinese study a few years ago claiming to have made metallic nitrogen.