Why are so many names based on folklore and such
Kishimoto is just a fan of Japanese culture and mythology. He's used loads of references, from Amaterasu, Tsukuyomi and Susano'o, to Izanami, Izanagi and Kotoamatsukami, to the trio of Jiraiya, Tsunade and Orochimaru, to the Sword of Totsuka and the Mirror of Yata, among many others. 

Many other mangaka have inspirations as well, not necessarily from Japanese culture, but from various other sources. A good example is One Piece, with many references. An example would be Usopp - taken from the Japanese word for lie (uso), Aesop (whose fable about the Boy who cried Wolf is the exact situation he's in when he's first introduced), and Pincocchio, as Usopp has a very long nose, like Pinocchio's, which grows longer whenever he tells a lie.