The stories make no sense on purpose

Coherence is the bug, not the feature.

Luc Beaudoin, a researcher at Simon Fraser University, proposed that the brain runs something like a gate on the way into sleep. The gate does not check whether your thoughts are pleasant. It checks their shape.

Orderly thinking — one thing leading to the next, a problem being turned over, a conversation being rehearsed — is evidence that something still needs handling. The gate stays shut. Thinking that wanders, that goes from a ladle to a harbour to a bolt of felt with nothing joining them, is evidence that nothing does.

The gate is not reading your thoughts for how nice they are. It is reading them for whether anything still needs doing.

This is why the stories go nowhere. There is no plot, no question raised in the third minute and answered in the eleventh, nobody whose situation improves. A scene is a place and some objects; then it is a different place and different objects, and nothing joins them: not a reason, and not even a colour.

It is also why they are deliberately not very interesting. Curiosity is a mild form of arousal. Wanting to know what happens next is a reason to stay awake, and a sleep story that hands you one is working against itself.

The uncomfortable part, which we would rather say than have you notice: a narrated audiobook is an inherently coherent, inherently interesting form, and we are using it to deliver a technique whose active ingredient is incoherence and boredom. The bet is that narration can hold attention without supplying a reason to keep listening. The rules every story is written to were tuned against that bet.

The longer answer

How strong the evidence is, and where it runs out, is in what the cognitive shuffling research actually shows: the one trial found people less wound up at bedtime, but it reported no figure for how quickly they fell asleep. Plotless sleep stories sets the idea against stories that keep a plot, and how a Sheeps story is made shows the rules each story is written to.