5. The History Is More Accurately Preserved and Easily-Accessible
Of course this is related to #1 above, but similar to the cultural immersion, the lengthy history of human civilization in the Pyrenees is much more in force and accessible on a daily basis. Instead of all of the ancient buildings that are still standing being relegated to tourist attractions and museums, the people of Spain actually use their historic buildings as everyday housing, bed and breakfasts, businesses, and restaurants.
In Bellver de Cerdanya I stayed in the old town, lodging in a bed and breakfast on the ancient town square in a building that was hundreds of years old—and still looked it. In the Alps, it seemed like many mountain towns featured a classic alpine wood construction, which precludes the age of enormous stone buildings like those found in the ancient villages sprinkled across the Pyrenees. Rolling into a town halfway through your ride and checking out a thousand-year-old church is an incredible experience that everyone needs to have!