Anyone who's worked in even the most windowed office building knows that only the spaces next to the windows get the light.

Plants need light to grow. The windows can only supply so much. So the other light has to be artificially produced (which eats energy).

The soil, the water, fertilization, etc can all be handled fairly naturally. But some of it will have to be imported. This is not "self sustained" by any means.

But the biggest factor is energy consumption. Is it cheaper to spend the energy to move crops from 100% natural light into the city or is it cheaper to spend the energy on artificial light and grow the crops inside the city?