Cancer, scale and component reliability.
The incidence of cancer does not vary wildly between species of very different weights. Thus larger species have much lower incidence per pound. Nature, when necessary, can produce tissue that is much less cancer-prone than that of mice, or men. Flesh is only as cancer free as it needs to be. However animals defend themselves against cancer, large animals have to do it better, and may be the best place to look for the mechanisms.
D000818:Animals; D005075:Biological Evolution; D001835:Body Weight; D006801:Humans; D009369:Neoplasms / Q000209:etiology*; D013045:Species Specificity