1) The modern process of food production has diminished its quality. Modern agriculture and intensive livestock farming have meant that food no longer contains as many vitamins and minerals as it once did. However, it still has the same number of calories.
We are therefore eating foods that are "not as nutritious as before." We need to eat more than our grandparents did to obtain the same amount of nutrients. Soils are becoming increasingly depleted and plants produce fruits and leaves with fewer vitamins and minerals.
The animals are fed with feed and grain instead of grass, and this causes their meat to be deficient in some vitamins.
2) The RDA (Recommended Daily Allowance) is not the ideal amount. It is only the amount necessary to avoid getting sick in the short term. To optimize health and reach your full potential, combat stress and the pace of modern life, the necessary amounts are much higher than the RDA.
3) Some micronutrients are even more beneficial if taken in larger quantities. This is the case of vitamin C. We are one of the few animals that do not have the capacity to produce it ourselves and it is a vitamin that plays a crucial role in the functioning of the immune system.
We lost the ability to synthesize it in an environment where it was not a problem, since ancestral fruits and vegetables had a much higher amount than current species. It was not a disadvantage, at least thousands of years ago. Today it is known that under stress conditions, mammals and humans consume part of their vitamin C reserves. But animals have an advantage over humans, they compensate for the losses by self-producing vitamin C again in their bodies. We do not.
It has been proven that a stressed goat is capable of producing up to 15,000 mg of vitamin C. And do they really recommend that we take 75 mg a day?
We, and most up-to-date doctors and nutritionists, see no point in this. And science agrees with us.