[yakubin]

In order to represent your walk vertically in a film, the camera would need to be overhead, directed at the ground (or beneath you, directed upwards). You walk forward from your own perspective, but it's rare from other people's perspectives (and still doesn't matter for horizontal vs vertical, since it's the Z dimension, not X or Y). Using depth to represent motion is a pretty bad idea most of the time, given that it's the dimension where movement is the hardest to notice (again, there are exceptions (precisely when you want the movement in the periphery to be hard to notice, only to make it more noticeable when the thing the moves gets closer (or the opposite))).

If you recorded Lord of the Rings, or Interstellar in portrait orientation, they would be pretty crappy films.

> the stuff I pay attention to when walking is more generally arranged vertically than horizontally.

I don't know what you mean.

Another point: your eyes are organized horizontally, not vertically. You have move horizontal vision than vertical. By filming in vertical orientation you quite simply make things more cramped, quite possible losing the space you could use to put more objects in, or just space out the objects you have in order to make things less messy.

Again, there are artistic reasons to sometimes prefer portrait over landscape, but that doesn't mean it's a good default. Making good films requires being conscious of those things, understanding that they are not arbitrary (therefore left just to which way it's more comfortable for people to hold their phones).