With respect to bikes (with or without pelicans) there's a strong natural bias because people displaying bikes tend to want to show off the side with the gears.

More-generally, I suspect an influence from how left-to-right languages (i.e. English) affect comic layouts. Overcoming that bias often means using vertical space to exploit the top-to-bottom habit instead. (Consider the rarity of an English-language comic panel where action is from bottom-right to top-left.)