Why is it in a lot of cartoons monkeys are portrayed as ninjas?

Do monkeys play a significant role in Japanese mythology/folklore?

goku

Son Goku from Akira Toriyama's Dragon Ball is based on the Monkey King from Journey to the West.

Monkeys do play a part in Japanese myth and folklore. Form wikipedia.com:

Monkey statues are also thought to guard against oni, since the Japanese word for monkey, saru, is a homophone for the word for "leaving". In Japanese versions of the game tag, the player who is "it" is instead called the "oni".

Making monkeys ninjas is logical.

Yeah like that Azumi movie the leader of the ninjas name was Saru and he was monkey like too.

But why is it in these cartoons he ninjas are the villians?

lol.

Well,from what i've seen,monkey's play an important role in japanese culture.But I beileve the monkeys are ninja because monkey's are swift,and mischevious creatures,like a ninja is swift and secretive ^_^