Quality effect, racial problem

If you haven't played the first generation, playing the second generation is a bit difficult to understand the plot:

Reaper, a mechanical civilization race that has existed since ancient times, is extremely powerful and advanced in science and technology. Every 50 thousand years, it cleans all the organic biological races in the universe and gains life. I don't know how many cycles have passed, so I call it the reaper. They are the most powerful force in the universe, and no one can understand their thoughts.

Collectors, originally a civilized race in ancient times, once developed a prosperous civilization. Later, when death invaded, they were defeated and destroyed. The rest of the people were transformed into semi-biological and semi-mechanical killing tools by the reaper, without self-awareness and became the lackeys of the reaper.

Why did the third-generation reapers invade the earth: The reapers will exterminate all the organic species. They chose human beings first because they have greater potential and will develop unpredictable changes. Harvesters like to control everything and are afraid of the unexpected, so they give priority to destroying human beings.

I'm tired of typing so many words. Take it.