Why Google's AI is Limited To Diagnosing Only 26 Skin Conditions for Now

It was recently reported that Google's AI system can accurately diagnose 26 skin conditions on par with US board-certified dermatologists. Results were published in the paper titled "A Deep Learning System for Differential Diagnosis of Skin Disease." The British Skin Foundation presents an equally extensive list. Google's AI System can only detect 37 percent of skin conditions using the list of 70 referenced above. So, if AI is so smart, why can't it detect all the skin conditions?