I am not sure of the mechanism that causes CNS fatigue, but obviously overuse of extremely intense movements can cause this.
Think of the CNS in regard to exercise this way. When you are doing distance running, each contraction of say the glutes is very weak, like the electric current it takes to move a second hand on a watch. Very low power output. Very low threshold motor units recruited, primarily type 1 fibers.
Second think of a set of 12 reps to fatigue doing a lunge. Mainly type II fibers are recruited, and they eventually fatigue. Like current that makes a huge searchlight illuminate. Medium power output, fatigue is not due to the nervous system, more blood lactate, hydrogen ions, things of this sort.
Lastly, a 3 rep deadlift. Like a bolt of lightning blowing your computers hard drive to bits. You will only be able to activate these motor units a few times at a maximal level. And when you do it is at an extremely high intensity.
The fiber typing in the glutes, and hamstrings to the best of my knowledge is very type II dominant. So you are using the biggest muscle in the body with the highest relative capability of generating maximal power. These motor units cannot be activated very often, I am not sure of the physiological reason.
If you should continously try to use these most powerful motor units its not like your body will get weaker, but it will not be able to show its true strength, it is saying, ok you want to do a deadlift, I can do a deadlift, but those motor units you used the other day? NAH, they are fucked, but you can use these! And usually you will see a huge reduction in power.