Simple: one of the basic requirements of being in power is wanting to have power. It's also one of the basic reasons one shouldn't be allowed to have power.
There's many answers but I genuinely fear they're too lost in the weeds of abstraction.
The truth is still simple; Power is useless to the common* (read: average and averagely distributed) person. It doesn't grow crops, shoe horses, or help your fellow man, inherently.
The common person has real concerns to worry about, leaving the search of the trappings of power for the uncommon.
Uncommonly good* (read: beneficial for the doer and the common person) is harder than uncommonly evil* (read: beneficial for the doer but detrimental to the common person); this is simply entropy, and it readily maps to humankind's so called capacity for thought.
That it only takes a bit of shared effort to make lasting structures to help others and fight off sociological entropy is an uncommonly good realization:
The common man has labors to do, the uncommonly good servant a statistical rarity and the uncommonly evil servants and the structures they engender to keep them in support (entropy begets entropy) a hurdle that by the point of realization takes an uncommonly amount of uncommon good to overcome.
TL;DR: Human nature + time + compounding apathy in those in a position to nudge things when they were easier to nudge = a need for collective awakening to course correct. We've gilded the lily on our sociological underpinnings but have yet to truly revolutionize, only iterate.