Why are many anime characters blond? There are a lot of blond-haired characters in anime, especially the old ones, like super saiyans, naruto, gundam series, fma, etc.
It depends on the culture, status of life (family) and the flow of the story. For example, the anime series of "Ikoku Meiro No Croisee" is used to have most character's blonde hair because the main story is that people lived in Paris. 

Some of the authors preferred to reflect it in the reality.