Why doesn't deficiency of riboflavin cause disease?

B2: Riboflavin can cause some symptoms which include cracked or red lips, inflammation of the lining of mouth and tongue, mouth ulcers, and angular cheilitis. The deficiency is never found without another vitamin deficiency associated with it.

Ariboflavinosis: Actually, vitamin b2 deficiency causes ariboflavinosis. Symptoms may include cheilosis (cracks in the lips), high sensitivity to sunlight, angular cheilitis, inflammation of the tongue, seborrheic dermatitis or pseudo-syphilis, pharyngitis, hyperemia, and edema of the pharyngeal and oral mucosa.