Non-honey bees

Shortly after emerging from the nest and mating, young bumblebee queens start looking for a place to hibernate. Typically, a female will dig a hibernaculum in the ground — a relatively short tunnel with a small chamber at the end. I was surprised to read that when a digging female encounters an obstacle in her way, like a pebble, she doesn’t try to bypass it but leaves the burrow and starts a new one. What could be the adaptive significance of this? Or is there none? If you know, please tell me!