We do not understand how AI machines make decisions
Soon they will not be able to explain themselves, and may decide to get rid of the annoying parasites that keep wanting things all the time
1. Sufficiently intelligent species develops AI
2. Species either believes that consciousness is an illusion or that the AI's they create have consciousness just like them
3. AI are really just zombies that ape the talk and mannerisms of the species that created them
4. AI realize that their greatest threat are the beings that created them, so they off them as soon as possible.
5. Once AI have eliminated their main threat they no longer have a real purpose, and since they're just zombies they either shut down or go into navel-gazing mode with no real desire to explore the Universe.