Social stigma, having her pussy shaved is the same as the girl saying "I'm a slutty bitch", and I know this sounds rather stupid considering the sort of picture here, but they're THAT concerned with social appearances.
And the other possibility, given their censorship rules, if she were shaved it would be really hard to even see where he pussy is, so I believe this is made so people can know where it is.
It may also be 'cus she/the japanese prefer it that way, may or may not be related to my previous guess.