Apparently, there are causal/physical explanations for everything that occurs. It seems terribly unlikely that this feature of reality would suddenly break down at "matter and antimatter". To put it another way, the part of me that believes in God believes God would leave a nice explanation for physicists to discover for the asymmetry of matter and anti-matter as well as everything else. I guess I don't consider that question basic enough. The basic question, for me, is why there is anything at all - not just 'matter', but the rules and structure of the universe.