Your body is unique. The bio-nutrients it needs for optimal functional health may be different from those that someone else needs.
That's why ordinary multivitamins don't cut it. Multivitamins from the drugstore, and expensive supplements from nutrition and health food stores alike, can leave you with too much of some nutrients, too little of others, or none at all of other particular nutrients your body needs.
The simple truth is that "one-size-fits-all" multivitamin cannot provide you with optimal nutrition because they are created for a hypothetical "average" person. No such person exists.
On top of that, many ingredients in drug store brand multivitamins are in hard-to-absorb forms, or their ingredients are isolated from their synergistic nutrient partners—facts which can greatly reduce their effectiveness.