It's not perplexing. The worst of humanity — the criminals, the psychopaths, the sociopaths, the pedophiles, the corrupt — are all attracted to positions of wealth and power.
Ethics and morality are complex/expensive. They can only exist in an environment of abundance. The only thing separating us from cavemen is education; the ability to document and transfer information across generations; the ability to produce excess resources than we need to survive. Self-sacrifice is basically rejecting those baser survival instincts of physical pleasure and worldly possessions for some ephemeral concept of "the greater good". That's what we need right now, but capitalism explicitly rewards the baser instinct of selfishness and greed with wealth and power, so the most greedy and selfish of humanity prevail.
It doesn't matter than civilization was built on cooperation or collective effort, or that selfishness and greed are a regressive, unproductive, dead end that will doom us all. Selfishness and greed only need to prevail long enough to destroy the foundations of civilization, like a stable climate and agriculture. Once those are gone, abundance ends, and we're back to focusing on our survival in hourly/daily increments.