But the Universe as we see it has some properties — and some puzzles — that the Big Bang doesn’t explain. If everything began from a singular point a finite amount of time ago, you’d expect:
different regions of space would have different temperatures, since they wouldn’t have had the ability to communicate and exchange particles, radiation, and other forms of information,
leftover particle relics from the earliest, hottest times, such as magnetic monopoles and other topological defects,
and some degree of spatial curvature, since a Big Bang that arises from a singularity has no way to balance the initial expansion rate and the total matter-and-energy density so perfectly.
But none of these things are true.