In that case we can just take Ozempic or whatever guys!

Just kidding, no that's not the problem. The problem is processing destroys/alter many molecules we do not even know about or know it's full "purpose"/role in nutrition and digestion. The commonly talked about vitamins and RDA and such are just the bare minimum so a broad population does not get sick, but does not mean optimum health for a given individual.

Cf. eating 10mg of iron in a steak, readily bioavailable vs eating 10mg of iron from cereal. One is bound in easily digestible compounds, the other is iron shavings or rust.

e.g The British Navy discovering that scurvy is fixed by eating fresh food; ensuring to add citrus to sailors diets, then forgetting about how it worked. Then retrying citrus, but cooking it one using copper vessels, which destroy much of the vitamin C content.