Vexillology

I think you generally avoid layering flags up like that. If you look at this Swedish flag for example, you can see that the yellow cross is made from three rectangular panels instead of just two, and the blue field doesn't extend underneath the yellow either. So while it could be made with one blue rectangle and two yellow ones, it has instead been done with four blue ones and three yellow ones.

I'd guess colours might not look right if they're layered up like that. Or maybe it's to keep it light so it flies properly. Not sure about the why, but it does seem to be standard practice