Because Chaos is power. Even the lowliest cultist understands this. What they don't know that they are foolish cannon fodder. You see, joining a cult shows that you are a weakling who needs someone to give orders. Cultists lost their chance of ascension the moment they joined the flock. The Gods prefer strong-willed individuals, not mewling sycophants. If I was a human of moderate wealth in the Warhammer 40k universe, I would seek out ancient texts to learn the art of sorcery (which even non-psykers can learn and use), experiment with the warp and focus on increasing my mystical and temporal power. I would create cults around myself, to help me achieving my objectives. They would be all dupes, ofc. Distractions for my enemies and the Inquisiton. I would see the Gods as patrons of a sort, so I would offer sacrifices for specific rewards but no useless ceremonies. Eventually, once I have enough power and knowledge, if I am not killed by the Inquisiton or experiments gone awry, I would try sacrificing entire worlds to achieve daemonhood. Given the harshness of life on most planets, it would be merciful to end their suffering this way. And If I get immortality out of it, that's just a plus. Ofc, It is most likely that I would be simply the antagonist of an Inquistion-focused novel, with the heroic inquisitor killing me just before my master plan comes to fruition.
Because we have buttered popkhorne, hot chocolate milked khorneflakes and skull-throne-o's with blood for kids.
