Possibly because there are many people out there with any number of problems (weight, depression, asthma, acne, diarrhea, rising of the lights,...) who, when mentioning those problems, are universally met with suggestions to change their diet. From someone who has no idea what diet the sufferer has.

But I'm with you, there, buddy. It's like these people don't even know rutabagas exist and supply all of the particulas vitae necessary for human existence.