Because meat comes from animals. And sometimes fruits and vegetables can carry bacteria on them, but those can usually be washed away. Meat comes from the muscles and internal organs of things like cows, chickens, pigs, and some other domesticated animals.

[The warmth of Grimmjow against his back makes Ichigo happy as he trims the fat from the chicken and slices it neatly.]

Not all domesticated animals are raised for food. Lots are kept as companions, some are even kept for protection. This meat is chicken, particularly the thighs of the birds.