Because heelside EC is notoriously more difficult to achieve. You're back to the bottom of the hill, can't see where you're taking the plunge, can't tell if there is going to be a straightliner on the other side etc... For me, at some level, that held me back (at least on steep), having to blindly commit to go head down below your board...so you look where you're going, you rotate the shoulder where you're going, but the bottom half of your body is screaming 'no way Jose!' and you end up with counter rotation and spectacular wash out...