Anytime discussion about the start of the universe comes up, the answer is pretty much always just "big bang". But that doesn't answer the more interesting questions of why did the big bang even occur and where did the matter come from? Why did all this matter exist in a tiny point before it expanded? It can't have just always been there, that is a non-answer. There must have been a state where no matter existed in our reality. Even if the singularity's mass was so great that time itself was not moving, it still does not explain the presence of mass to begin with.

Are there any leading theories that explain this? Simulation?