When the touchpad is set to emulate a mouse scroll wheel while using a circular gesture, swiping clockwise is scroll down and swiping counter clockwise is scroll up. Of course, you can change this if you want:
Steam>Settings>Controller>Pair and Manage>Desktop Layout>Edit>Edit Layout>Trackpads>Left Trackpad Behaviour>[gear icon]>Invert Swipe Direction
Or just swap the "Clockwise Command" and the "Counter Clockwise Command" under Steam>Settings>Controller>Pair and Manage>Desktop Layout>Edit>Edit Layout>Trackpads>Left Trackpad Behaviour
But regardless of the fact that it can be changed, there must be some logic to why the Steam Deck touchpad behaves that way by default, right? Help me make sense of why some dev team at Valve decided that the default should be "clockwise=down" despite these other common scenarios in which "clockwise=up".
Makes sense. Let's say you are standing with a tower directly in front of you. If you want to look at the top of the tower, you would tilt head back and step back to get a less acute angle. If you want to look at the base, you would step forward.
I find it the most intuitive when thinking about flying a plane.
If there is one stick to control the plane
Imagine a toy plane on top of the stick
To make the plane climb in altitude you'd tilt the back of the toy plane down and point the nose up. That would mean pulling back on the stick.
Now if you stick a head on that stick. To make it look up it would be the same. Pull back.