i think it might be a subtle anatomical oversight, the way you've depicted where the hips and buttocks would be means
his left leg is being twisted outward, or his right leg is a tad longer than it ideally would be, when people cross their legs, unless they twist the under leg inward toward the other, they can not hook their over leg on their opposing leg, some people aren't even flexible enough to tilt their legs inward enough to do so, but
here is a picture of the source inspiration to illustrate it somewhat. and
here is an extreme yet entirely un-edited example of the twisting needed to pass legs further up than the knee (looks quite unnatural)
and here is a quick edit with some suggestions on how to improve without too much effort:
