It may have to do with language.
The idea that language influences thought is called Linguistic Relativity:
The more accepted weak version claims that linguistic categories and
usage only influence thoughts and decisions.
Lera Boroditsky summarizes research on the influence language has on direction and time:
English speakers tend to talk about time using horizontal spatial
metaphors (e.g., "The best is ahead of us," "The worst is behind us"),
whereas Mandarin speakers have a vertical metaphor for time (e.g., the
next month is the "down month" and the last month is the "up month").
... Imagine this simple experiment. I stand next to you, point to a
spot in space directly in front of you, and tell you, "This spot,
here, is today. Where would you put yesterday? And where would you put
tomorrow?" When English speakers are asked to do this, they nearly
always point horizontally. But Mandarin speakers often point
vertically, about seven or eight times more often than do English
And in more detail in a Scientific American article:
... my colleague Alice Gaby of the University of California, Berkeley,
and I gave Kuuk Thaayorre speakers sets of pictures that showed
temporal progressions—a man aging, a crocodile growing, a banana being
eaten. We then asked them to arrange the shuffled photographs on the
ground to indicate the correct temporal order. We tested each person
twice, each time facing in a different cardinal direction. English
speakers given this task will arrange the cards so that time proceeds
from left to right. Hebrew speakers will tend to lay out the cards
from right to left. This shows that writing direction in a language
influences how we organize time. The Kuuk Thaayorre, however, did not
routinely arrange the cards from left to right or right to left. They
arranged them from east to west. ... in Aymara, a language spoken in
the Andes, the past is said to be in front and the future behind. And
the Aymara speakers’ body language matches their way of talking: in
2006 Raphael Núñez of U.C.S.D. and Eve Sweetser of U.C. Berkeley found
that Aymara gesture in front of them when talking about the past and
behind them when discussing the future.
This suggests that if you reversed the exercise, binding the left/right keys to movement forward or back, then you might get different results from Hebrew speakers than English ones. And if you presented this exercise to speakers of Kuuk Thaayorre, then the results might depend on which way the keyboard is oriented - ie, you would get different results depending on whether the keyboard faces East or West!