I always enjoyed the reveal during the suicide mission that >! theyre creating a Human Reaper. Sovereign tells you in ME1 that theyre the peak of evolution, Mordin muses on the Collectors that the Reapers have stripped them of everything - culture art, even their original biological function - for their own purposes. Also, that they have no challenge to respond to so they just stagnate. My headcannon was always that the Reapers are that, too. The Reapers reached such a position of unchallenged preeminence and dominance that they've essentially looped and became animals again, they literally dont care about anything other than the means of their reproduction. They're the dominant form of life, and they'll drag you into the future, make you like them, whether you like it or not. They're literally the future!<

of course all that changes in ME3, but still lol.