[anigbrowl]

Conjecture, but I believe this is due to disordered preference for orienting oneself perpendicular to converging lines. Imagine yourself standing on a long straight road. Now imagine yourself looking over the side of a building, which is equivalent to looking along a similarly flat surface but from a much reduced height, as if you were lying on the road and trying to look at it over the tops of your feet.

A maladaptive orientation instinct might be caused by overcompensation for astigmatism or other distortion, or a strong preference for one kind of visual cue (converging parallels) over another (the more abstract knowledge of gravity and the associated impacts.

There is some evidence to suggest that premature babies are more likely to be subject to such disorders. https://en.wikipedia.org/wiki/Visual_cliff

[CuriousCosmic]

The problem is that l'appel du vide does not just apply to jumping off a cliff. It tends to pop up in situations where somebody could take a very simple yet extremely dangerous or guaranteed life-ending action. The other common case of l'appel du vide is the thought of just letting the car swerve into a tree or pole.

[anigbrowl]

I know, but I don't think that is the only factor in play. You could have vertigo without ever having the inclination to step in front of a train.

[taneq]

If that were the case then it wouldn't also result in, say, fantasizing about swerving off a straight road into a tree.