Because most food poisoning is bacterial, not viral. When a virus is erroneously referred to as food poisoning (Norovirus), you actually get it through traditional viral infection methods, like eating after infected person (spit) or hand to mouth. Noroviruses have evolved a special mechanism that targets an obscure gut cell, which is what causes the vomiting and runs, but they don’t ride in on infected food but contact with infected surfaces or cups. (Micro fecal matter or saliva).
Most viruses get destroyed by digestion, they must get in via the usual methods of blood, saliva or blood in mucus membrane in your nose, eyes, mouth, lungs.