Why do dogs have to pace back and forth to poo?

My dog does this too and its not always the same spots. Its amusing to see them have to find that right spot, but I wonder why do they sniff all around and then pace back and forth or spin in a circle to finally go, sometimes shuffling up a foot or two after they began the process. As if in the last minute that spot became tainted.
Does really wondering. Whats with the last minute change? Is it the smell on the ground or the wind direction that changes their mind?
I know this seems silly, but I’ve been walking my dog for 12 years and still don’t know what is he narrowing in on.
Maybe if I can figure it out than I can take him to a spot he will figure is a goldmine and I don’t have to stand out there in the cold so long, waiting for him to find the secret garden.