Over-illumination stems from several factors:

Not using timers, occupancy sensors or other controls to extinguish lighting when not needed
Improper design, especially of workplace spaces, by specifying higher levels of light than needed for a given task
Incorrect choice of fixtures or light bulbs, which do not direct light into areas as needed
Improper selection of hardware to utilize more energy than needed to accomplish the lighting task
Incomplete training of building managers and occupants to use lighting systems efficiently
Inadequate lighting maintenance resulting in increased stray light and energy costs
"Daylight lighting" can be required by citizens to reduce crime or by shop owners to attract customers, so over-illumination can be a design choice, not a fault. In both cases target achievement is questionable.
Substitution of old mercury lamps with more efficient sodium or metal halide lamps using the same electrical power
Indirect lighting techniques, such as lighting a vertical wall to bounce photons on the ground.