"Why is there something rather than nothing?" is a special case of the question "Why does the universe behave this way instead of some other way?" Answers to questions of this kind appeal to some model of the universe, providing general rules that apply in a specific case; for example, apples fall because of the general rule of gravity.
Better answers are both simpler and explanatory of a wider range of phenomena. An ultimate Theory of Everything (TOE) would explain every phenomenon. The TOE would be an answer to "Why is there something rather than nothing?" - the answer being, because the universe follows these equations laid out in the TOE, and the equations predict something rather than nothing.
But that might seem unsatisfying. You might demand some reason the TOE is the way it is. This would be some formula or proposition - simpler or more fundamental than the TOE - that has the TOE as its consequence. In effect, this formula or proposition would itself be a simpler TOE.
But there is going to be some irreducible complexity. The TOE is not going to be a formula of length 0. It's going to be at least a few equations.
And this irreducible complexity is the limit of our ability to ask "Why is the universe like this?" We can't give any simpler or more fundamental answer than the simplest possible TOE, and the simplest possible TOE has nonzero complexity.
So ultimately the answer to a chain of "whys" has to be "just because that's how it is." At the end of a chain of "whys" you will always find some irreducible complexity that can't be explained in terms of anything simpler.