There is a fine line between flossing and snagging (pardon the pun). Flossing is 'upper class' snagging. That means the fish is hooked in a location and in a manner that is identical to how it might have been hooked if the fish had taken the fly, if it were a willing biter, even though it's not.

But snagging is just snagging.

The reason for the rule on 'hook placement' is to maintain that distinction.

I'm not defending the rule, just stating the reason for it's existence.