[pagan queen]

If you consider other animals, their young all grow fast and soon become independent. Most animals have the protection of their parents until they can defend themselves or fly/run to evade capture. Tortoises, although faster than most people think, could not out run a crow for example. Their only defense is their shell and camouflage. The shell can easily be penetrated by a bird or chewed by a fox/badger etc. Their camouflage only protects if they don't break cover and has minimal effect against ground dwelling animals like snakes and rats.
So the best form of defense is to grow to such proportions that the number of predators is reduced by the very fact that they can no longer pick up the animal or penetrate the shell as easily. A six inch tortoise is unlikely to be eaten by a crow. Many birds, seagulls, crows etc have learned to pick up and drop shelled animals from heights to crack open the shell. Even blackbirds and thrushes could eat a hatchling by smashing the shell open on a rock in the same way they open snails. So nature has provided them with protection just like it has for all other animals. So, to restrict food and grow them slowly is going against nature and therefore can't be beneficial to the well being of the animal in the long term.