It's because in Victorian times well-to-do ladies and their gentlemen escorts would take the steam train to the top of Mount Snowdon to enjoy the spectacular views, riding in open-topped carriages and more often than not having sudden strong breezes near the peak of the mountain whisk away the hats of those not taking care to be holding onto them in those open carriages.
Local farmers, miners and other villagers living below in what eventually was to be officially called Cwm Hetiau (The Valley of the Hats) would boast that their wives and daughters had the best collections of hats in Wales – and that it had never cost them a penny to see their ladies so finely attired for Sunday outings.
FOOTNOTE: IF you've ever wondered at the expression "Mad as a Hatter," it was because in the 18th and 19th centuries mercury was used in the production of felt for making hats. Small traces of this mercury could be slowly absorbed by hat makers, accumulating in their bodies over the years and causing some to develop dementia that was dubbed "Mad Hatter Syndrome" – and eventually applied as "Mad as a Hatter" to anyone showing signs of insanity.
 HISTORIC open-topped little train in Wales. (Photo: Snowdon Mountain Railway.)