I don't know why, but the big bang does not sit well with me. Not from any scientifically informed perspective, it doesn't seem right to have something that finite.
I don't think anyone with a scientifically informed perspective pretends they know the big bang was finite in nature. We're just inferring based on our understanding of physics and our observations of the universe that what we perceive as the universe seems to have grown from an ultradense, unfathomably energetic smaller point. We have no idea what, if anything, came before, or whether there are other universes besides our own