And the original gods weren't even supposed to be causes of the world-as-a-whole - they were just anthropomorphic hypotheses to explain aspects of the world.

However, that sort of thinking eventually got us to the point of asking about where existence as such, the world as a whole, came from.

Which in turn - thanks to basic questions like the one you just asked - led to concepts such as "first cause" and "necessary being" and so forth.

So, the human race already has had a few ideas regarding why existence exists. You may not find any of them persuasive. But my real point is to warn against complacency. Rationalist materialists such as congregate on this site have a deplorable tendency to regard some combination of mathematical physics and quantitative epistemology as a closed and complete philosophical system, and they need a periodic prod in the third eye to remind them that there are questions which are not addressed even in principle by that particular synthesis - and that it is possible to think about them, rather than just rationalize them away.