Interesting factoid: modern guitar effects typically have their input jacks on the right-hand side, and output jacks on the left. In this article's guitar rig diagram, the jacks are reversed, but this is accurate: back then, for whatever reason the jacks were reversed on each of these pedals. Modern reissues of the round-enclosure Fuzz Face pedals preserve this pattern despite the reversal of industry trends.
It does seem weird, I’d expect signal to flow from left to right, as English is written, as a number line is drawn, from -x to 0 to +x
the ergonomic advantage of left-to-right is that most players use right-handed guitars, so the guitar's cord comes out the right side of your body, and it's most ergonomic for it to be directed straight away from you to the right side of your pedal board, not criss-crossing in front of you towards the left side of your board.
With your cable in your right hand, it is easier to plug into the right side of a pedal. If you were to try to do the equivalent with your left, the guitar neck would be a little bit in the way as well.