system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why does it take time to fall asleep and we can’t force it consciously?

Other brain activities like focusing, reading, remembering and so on, can be triggered actively whenever we want, but we can’t decide when we fall asleep. Besides some specific conditions must be fulfilled, like being tired, in a relaxing position, appropriate light...
gpt
Maybe because sleep is not the same type of brain activity. Quite the opposite, sleep is a major change in brain activity. 

We are evolved animals but still animals. A lot of those conditions are evolutionary adaptation for survival. 

On the other hand there are techniques and routines that help people fall asleep faster. A common problem is a tendency to engage in thoughts and worries. That’s a bad habit that can be trained out.