Why do dogs still fear lightning?

I type this as my two dogs cower in the basement while lightning rages all around the house. The Labrador retriever cowering I understand (she is temperamentally sensitive), but it never stops being odd to see my otherwise fierce German shepherd afraid as well. I understand that loud sudden noises are an instinctual fear in humans and likely most other mammals. It is common for small children to fear thunder but eventually outgrow that fear. At 10 & 11 years old it is clear that neither of my dogs will be outgrowing their fear of thunder. Labradors and German Shepherds are both highly intelligent breeds. It must have occurred to them that in all their years of life, not once has thunder ever harmed them. I can’t help but wonder what it is that humans have and dogs lack that allows for outgrowing the fear of thunder.