Food spoils due to many factors, mainly the amount of preservatives, moisture and air levels and temperature. If the preservatives are the same in both, then I would say that the higher amount of moisture and air in bread is the cause.
In any case, keeping it in the fridge will extend both products lifespan, although it is recommended to keep bread in an airtight bag at room temperature for best quality. Tortillas seem to be fine in the fridge, and can stay good for weeks!
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