Why do simple machines not reduce the total amount of work required?

Simple machines do not reduce the total amount of work required because they function by modifying force and motion, not by creating energy. In physics, work is defined as the product of force and the distance over which that force is applied ($W=F\times S$).12

When you use a simple machine, such as a lever or a pulley, you may gain a mechanical advantage by increasing the output force, but this gain is always accompanied by a proportional loss in the distance over which the force must be applied. Essentially, what is gained in force is lost in motion.13

Furthermore, because of friction, the actual work output of a machine is always less than the work input. Machines are designed to make tasks easier by modifying how force is applied, but they cannot bypass the fundamental principles of energy conservation; they simply redistribute the effort required to perform the same amount of work.314