“Why is there Something rather than Nothing” ?
What are the constraints ? What reference system is imposing what constraints on reality, the universe, its design, its logic, etc. ? None, and in fact questions like this imply some external, more general reference system where some kinds of laws or logic, some constraints are operating such that there must be some kind of logical answer: nothing further from the truth, the more general reference system, the superset where the universe or/and our logic, language, or the Principles of Identity and Non Contradiction are operating is a subset of, is a system where absolutely anything goes: even an answer like "NO REASON AT ALL", or "JUST BECAUSE" or anything else you can imagine.
The fact is we cannot imagine or contain a reference system that doesn't have logic, non contradiction and is void of cause and effects, whereas this is exactly the reference system where the universe and our laws of physics are delimited in: and this reference system is so general that it has no space or time constraints, no existence constraints, no constraints at all, or constraints which are way beyond our capability to conceive: and in fact the typical answers such as the "higher probability of something against nothing is the reason why there is something" implies that you are already within a smaller, simpler, more limited subset and reference system compared to a free and non constraining general reference system, implies that cause and effect and non contradiction are operating, but that already simply brings us back to our universe anyways, whereas the answer to why there is something and not nothing is outside of our logic and universe and even outside of any of our language and constructions and thought processes and such. In other words, it is even outside of the concepts of Questions and Answers, the question can have any and no answer at all, and you are free to lie, as saying non truths and lies and contradictions is the only way to begin to approach these kinds of problems, if they are even problems, if they are even questions and such.
Hence, why something and not nothing ? Just Because, FOR NO REASON AT ALL.