Same reason it happens to us
like clockwork. I've about given up on prefishing for this reason haha. I do some much better when I "just go fishing".
I learned a great lesson back in college when Jason Christie met with our team. He used a great example- Say you are prefishing and find fish in an a specific are. When tournament time comes and the wind has changed, where are you going to fish? Right where you found those fish and you pretty much throw out the current conditions. Where if you were "just fishin" you would pull up to that windy bank on the other side of the cove and find the fish there. Not 100% accurate but you can definitely get the picture