On the Big Bang theory: For every one billion particles of antimatter there were one billion and one particles of matter. And when the mutual annihilation was complete, one billionth remained - and that's our present universe.
"If you attempt to detain me I shall destroy your entire planet! The engines of my starship are powered by Anti-Matter, a substance opposed to everything that matters in the universe. If I were to release the magnetic forcewall which separates this Anti-Matter from normal matter, the resulting explosion will turn your planet into a heap of gravel! After all, why should Earth look different from other worlds?"
— Plan 7 of 9 from Outer Space
Critically, a nuke will only explode if you want it to, whereas antimatter is always trying to explode whether you want it to or not.