The short answer: Using reason alone, an intellectually honest answer is very, very difficult.
The longer answers:
(1) The fact that you are a conscious, intelligent person asking this question already speaks volumes. Why? Because intelligence is not native to matter and intelligence certainly is something.
(2) Scientifically speaking, your question poses a challenge because there is no field that specializes in ontology. Even the most cutting-edge fields today adhere to a myriad of nature-given laws but there is not an answer as to why said laws exist in the first place.
Even more, we are able to discern what is true based on the senses and then using that data to develop models which can then be used in reality-testing. The problem with proposed transition from nothing to something (or an eternal something to something) is that no one was there to observe what happened and why. So while while the sciences have provided tremendous insight, any theory as to why something resulted from fluctuations of nothingness is at best speculative.
(3) Certainly, there are answers that are reductionist such as, "Why not?" but this ends up being to overly plain: it doesn't answer your question nor does it satisfy intellectual curiosity.