People at that time would wander around a lot in their everyday life, and it would be very easy to remember these small stories which are connected to the landscape. A father would tell his son when they were walking past this feature of the landscape, and the son would later tell his son and so on.

Why? Because they didn't have cell phones to scroll on while wandering, or a radio to listen to. And they weren't thinking about their mortgage or about primaries. When you live in a world like this, it is very easy to remember a bunch of unusual stories, and when they're connected to the landscape instead of to people, it is almost a guarantee that they will be passed on for generations.