I can remember when the notion of what was before the big bang was universally dismissed as a nonsensical question, but that is not the case any more.
There are even hypotheses of e.g. an inflationary period happening before the big bang, and corresponding predictions about the macro structure of the universe.
But, of course, the real reason so many people bring up the issue of “before the big bang” is because what they are really getting at are philosophical questions of how come anything exists at all.
And that’s something beyond our current understanding, maybe it always will be – could we ever explain something without mentioning prior states or pre-existing laws?
(This is not to advocate religious explanations. I’m an atheist and for me “OK, first there was a god…” clearly doesn’t help in terms of explaining why anything exists)