Nice try, I'd also like to know. But I am afraid no-one here will be able to answer you. But maybe we're lucky -- I'll monitor this thread.
We can never know the answer, because any possible cause was outside of our observable universe. Inside of our universe, time started at the big bang, so there was no 'before' and thus there was no cause, because the cause needs the time to be before the effect.
Well, if it's true the universe will start contracting at some point (which, some speculate, could happen sooner than we had thought[0]), and if a big crunch leads to a big bang, it is not impossible that this very moment - in the sense of these actual circumstances we're in - already happened an infinite number of times. (Still doesn't really answer the 'why?')
We can never know the answer, because any possible cause was outside of our observable universe. Inside of our universe, time started at the big bang, so there was no 'before' and thus there was no cause, because the cause needs the time to be before the effect.