The Big Bang “theory” was wacky speculation from day one.
If they had called it the Big Bang Hypothesis that would have been a better representation of what was happening.
I suppose if you choose to ignore all the evidence supporting the Big Bang theory, it might seem unlikely. But it exists in abundance despite not knowing about it. The theory itself does not necessarily say the universe started from a singularity at a specific point in time. That is extrapolated based on what we see today, and based on predictions that have been observed after the fact. But if there is another theory that better matches observation, no one has yet proposed it. By the way, it was not originally called “Big Bang”. That is a term coined by someone who was not a proponent of it and didn’t understand it.