Why Standard Lenses Can't Use Macro Focal Ranges
Macro lenses exist because standard lenses cannot enter macro focal ranges. This predicament is due to a physical impossibility in the structure of a standard lens.
In a standard lens, each glass element is fixed in its relationship to the other glass elements. As you focus, you move all the elements either farther away from or closer to the film plane. Due to this rigid design, these lenses are limited in the range of focus that they can achieve. In macro lenses, the glass elements "float", which opens up the realm of possibility.
Complications with Light
When you use a standard lens and focus at its closest possible plane, you will notice that the barrel has extended itself. This is necessary in order to focus on multiple planes, and part of the reason that the lens is designed to stop where it does is problems with light. The extra length creates more distance between the glass and the film plane. With so much distance, only a fraction of the light will actually reach the film plane, and the rest will be caught in the lens causing hazing.
Creating a macro lens requires entirely different optics than a standard lens. Otherwise, the physics simply do not add up.