I agree with your points about distinguishing questions from meta-questions, and about not expecting an answer in our lifetimes, but respectfully, I’m not sure you have been careful in regards to placing a stop sign at this specific question. As I’m sure you know, the big bang framework is not a theory in the physics sense, and there have been many models of how it might have worked in practice, each with different implications. We already have observational data that doesn’t quite fit many of the implications many big bang models and inflation models would imply - flatness, baryon asymmetry, the cosmological constant problem, low entropy initial state, and various questions about quantum gravity (the latter two being potentially closely related to what the universe’s apparent arrow of time even is, and whether fundamental physics is timeless). It is not at all clear that further investigation of these more concrete problems might not push the veil back a few steps further, and even if there is an infinite regress of questions, it isn’t clear we’ll ever be able to determine that a given one is unanswerable.
Personally I’m inclined to think in terms of Tegmark’s level 4 multiverse - that “existence” is not some additional property somehow tacked on, it’s just what a coherent mathematical structure feels like from the inside. That would fundamentally dissolve the question of why anything exists or why this specific universe exists. It would reduce the problem to “Everything exists, and the rest is the question of what types of beings have higher measure in what type of mathematical structures.” Physics questions become the indexical uncertainty of not knowing which structure we are part of.
