If you turn a sausage machine backwards, you don’t get a pig coming out the top.
If I add a dozen numbers together, there’s only one total.
But if I only have that total, there’s no way to tell what the original dozen numbers were.
Same kind of principle.
You can brute-force it, but when it comes to the product of stupendously large primes, it would take until the heat death of the universe to do so, by which time you probably don’t care any more.