As James Peebles pointed out in a conference after his Nobel Prize in 2019, the term “Big Bang”, which connotes a creation in a place, at a specific time, is a misleading term.
If, for the standard cosmological model, Einstein’s equation defines a spacetime which implies a singularity, which, moreover, is not part of this spacetime, to interpret it as a beginning to this spacetime is an anthropomorphic nonsense!
A spacetime does not need to be localized in something which would define a time reference and a space container. The phenomenology of the universe can therefore be defined, only, by internal geometric properties of this spacetime.
Thus expansion, for instance, is an internal property: The geodesics followed by the infinitesimal elements of the fluids filling the universe, all emerging from the vicinity of the singularity, diverge.
So, the universe has neither creation, nor past, nor present, nor future and is not expanding, the only sensible problem is that of its existence. Because we are part of this universe and because we exist, the answer is a tautology: The universe exists.