They don't have the kind of athletes on offense with the physical talent to create offense for themselves. Diggs, as great a technician as he is, has the athleticism of a 5th rounder. He runs phenomenal routes and has great hands but he isn't a real threat after the catch. Davis, similarly, is a fourth rounder. Knox a third. McKenzie and Shakir are both 5th rounders. The Bills just don't have guys on offense with the kind of elite athleticism that can succeed outside play design or scheme.