There is no literature component for any AP modern foreign language exam (AP Spanish Lit being a separate exam).
I don’t think that’s the reason. The schools that don’t give credit for AP Chinese usually also do not give credit for AP Japanese.My guess is that those colleges do not equate the level AP tests for Japanese/Chinese to be comparable to Spanish/French/Italian/German.
But for the OP, I agree with the others; you can take it for possible placement/exemption for college, but don’t use it as one of the required/recommended Subject Tests.