Y did the USCIS denied my I 129f

I understand you you are frustrated by this situation but without reviewing the actual decision it is impossible to provide an answer. USCIS will send a written decision explaining why the Form I-129F was denied. You should have the decision reviewed by an attorney to determine how to best proceed. You can read more about fiancé visas at  http://myattorneyusa.com/k-1-and-k-2-visas-for-fiancees-and-derivatives.