Presumably it's pleasant the rest of the time, or near a suitable travel route or natural resources, and because it's easier to build there than higher up the mountain side.

E.g. while much newer, the town of Rjukan in Norway which also has a small heliostat, was built specifically due to the nearby waterfalls that provided easy access to power for industrial use, and the valley floor was where most of the town was constructed because that's were the easily accessible terrain was.

It's a small hamlet founded by iron miners, they were familiar with darkness. Foundries and blacksmiths also worked well in the shadow i think.

Here is a quick history of the village https://www.comune.borgomezzavalle.vb.it/en-us/vivere-il-com...

I assumed it was a safe place to live in the year 1300 through the 1800s when Napoleon was romping through Italy on through to the 1940s.