Why is there anything? It is kind of conceivable that there could be no thing 'existing' at all – no world, no universes, no consciousness. However, there is at least something.
Let me clarify the question: The opposite of “there is something” is “there isn’t anything (e.g. observed)” but not “there is (e.g. observed) some nothing”. This is important to avoid much ado about nothing. “Nothing” refers to the absence of anything. “Nothing” is not another something.
If nothing were another something that “is”, this “something” would have to “be” precisely in case there is not anything (a contradiction). This contradiction is not the answer; it is nonsensical to claim that there is either whatever else or there is still nothing, so something is always there, even if that something happens to be nothing. Such is crazy talk confusing different meanings of 'exist'.
The correct answer is: Because it is possible!
If the posed question were about any other system but totality, this answer would be wrong: That something is merely possible does exactly not imply that it is necessarily actualized.
As philosophy, we are still unable to fully grasp the answer. Physics presents it in a more acceptable form, although physics could have been expected to be the least likely science to do so: Physics, the science that started out to be squarely about things bumping around inside a world, but ended up showing that there are no such things or such world.
Quantum mechanics brought the posed question into the realm of science. Although it is a pseudo question that depends on what you mean by “exist”, quantum mechanics kind of answered it anyway. It thereby turned the posed question into a lesser one:
Why is anything possible? This question we may be able to answer, once fundamental physics rests on epistemology, as it must, since all else is upside down.