Can we explain the mystery of existence? But, of course, the most we can arrive at is certain ideas about why we others, and various life forms exist. These ideas are our perceptions and perspective, and are only partial. — Jack Cummins
I was thinking about "WHY" question again, and it seem to me that "WHY" only exists in human mind. Once we are looking outside world, there is no "WHY" at all. So, when you ask "why" questions, it can only be answered from one's direct experience about something, or one's own feelings and motives.
So when why question is asked for the universe and other lives existence, the answers will have to come from only from one's mind, which is either reasoning, imagination, or experience. Once we go out the boundaries of our reasoning, all the explanations and questions disappear. The universe keeps working as it has been for billions of years in silence, and live come and go living their own times without any reasons and explanations.
In the case of the question, if you seek the answers from science, history or religion, then the answers would be based on the First cause, or the Big Bang theory or Creation Theory by God, or Evolution Theories, but I would imagine these are not the type of answers that you wanted to hear or accept as the right answers for the question.
But it does not mean that we have reached the ultimate answers or knowledge, because thoughts always start in the middle and ends in the middle. When Kant has finished his CPR, he thought he had reached the ultimate knowledge and solved all the problems in Philosophy and Religion. But he was wrong. There came the Neo Kantian schools, Hegel and German Idealism, then Phenomenology. It all seems just a part of the process.