Answer from evolutionary theory
Judging by the drawing they have very small penii. For that reason the males have to grow large ears to impress the females. It's a matter of sexual selection.
EDIT to add example
by the time Homo erectus arrived on the scene, the hominid penis was significantly longer, fatter and more bendy than our ape cousins'. It
has even been theorised that bipedalism evolved in humans to allow the
fashionably new, larger, flexible penis to be displayed to discerning
females Penis size: An evolutionary perspective - Carole Jahme
Of course the above puts forward only one theory. However when our forbears ran naked, like the Panotti, the penis would have been in full view.
... when the males and females of any animal have the same general habits ... but differ in structure, colour, or ornament, such differences have been mainly caused by sexual selection ... Charles Darwin.
The fact that their ears are now ridiculously large is a consequence of
Fisherian runaway or runaway selection is a sexual selection mechanism proposed by the mathematical biologist Ronald Fisher in the early 20th century, to account for the evolution of exaggerated male ornamentation by persistent, directional female choice.
Here's a real life example of extremes in outward facial structure that serves no purpose other than display: