The question of why there is an asymmetry between matter and antimatter in the universe is still an active area of research in physics. It is indeed a puzzle why the Big Bang didn't result in equal amounts of matter and antimatter annihilating each other, leaving behind only energy.
One possible explanation is a phenomenon called "baryogenesis." Baryogenesis refers to processes that could have led to a small excess of matter over antimatter in the early universe. These processes involve violations of certain fundamental symmetries, such as the conservation of baryon number or the violation of charge-parity (CP) symmetry. The details of baryogenesis are still not fully understood, and several theoretical models have been proposed to explain the matter-antimatter asymmetry.
Another related concept is "CP violation," which refers to a violation of the combined symmetry of charge conjugation (C) and parity (P). CP violation has been observed in certain elementary particle interactions, but the amount of CP violation observed so far is not enough to explain the observed matter-antimatter asymmetry in the universe.
These are active areas of research in particle physics and cosmology, and scientists continue to study the matter-antimatter asymmetry to better understand the fundamental nature of our universe.