My answer to the question of "Why is there something rather than nothing involves first providing a reason for why anything exists and then showing that what has traditionally been called "nothing" meets this reasoning and therefore really isn't "nothing" but actually exists.
In regard to the question of "Why do things exist?", I suggest that a thing exists if the contents of, or what is meant by, that thing are completely defined. A complete definition is equivalent to an edge or boundary defining what is contained within and giving "substance" and existence to the thing.
In regard to the question of "Why is there something rather than nothing?", "nothing", or "non-existence" is first defined to mean: no energy, matter, volume, space, time, thoughts, concepts, mathematical truths, etc.; and no minds to think about this lack-of-all. Next, I propose that this "non-existence" itself, and not our mind's conception of non-existence, in and of itself completely describes or defines the entirety of all that is present. Therefore, as a complete definition of what is present, what has traditionally been called "nothing", or "non-existence", is actually an existent state. That is, what has traditionally been called "nothing" is, when seen from a different perspective, an existent state or "something".
Another way to reach this same conclusion is by saying that in regard to the question of "Why is there something rather than nothing?", there are two choices for answering this question:
A. "Something" has always been here.
B. "Something" has not always been here.
Choice A is possible but does not explain anything. Therefore, choice B is the only choice with any explanatory power. With choice B, if "something" has not always been here, then "nothing" must have been here before it. "Nothing" is defined as above. But, in this complete "nothing, there would be no mechanism present to change this "nothingness" into the "something" that is here now. Because we can see that "something" is here now, the only possible choice then is that "nothing" and "something" are one and the same thing. This is logically required if we go with choice B.
Now, instead of saying "That can't be. Something and nothing are not the same", it's better to try and figure out how these two logically-required equivalent things can really be the same. The reason, I believe, is as described above that what has traditionally been called "nothing" completely describes, or defines, the entirety of what is present, and is therefore actually not "nothing", but is really an existent state.
Overall, I come to the conclusion that many others have come to which is that having true non-existence is not possible because even what we have traditionally thought of as true non-existence is really an existent state when seen from a different angle. Non-existence is basically a misnomer that has come about because we've been thinking of non-existence in our minds, which exist. Next to our existent minds, nothing just looks like nothing. But, nothing, or non-existence, itself, and not our mind's conception of non-existence, isn't dependent on being defined as the lack of existence. It's on its own and, on its own, completely describes the entirety of what is there and is thus really an existent state. In this (and all) areas, it's very important to distinguish between our mind's conception of non-existence and non-existence itself in which all minds along with everything else are gone.
This may all seem to be a waste of time, but the above reasoning provides a reason for why things exist and by trying to figure out the properties of the particular existent state previously referred to as non-existence allows one to build a model of the universe that is based on these properties via what I call "philosophical engineering". This model has symmetry breaking, a natural reason for why energy exists and a big bang like expansion of space.
A more thorough discussion of the above idea along with some responses to critiques is at my website at: https://sites.google.com/site/ralphthewebsite/filecabinet/why-things-exist-something-nothing
Also, some discussion of this has also taken place recently at google.com/groups in the epistemology and everything-list groups and many years ago at a digital philosophy group.