I'm pretty sure it's due to exactly that sort of hubris that business school folks have invited so much disdain. The domain in which you're operating simply cannot be dismissed as an inconsequential detail.
Tangentially, there is a subset of law firms that do operate as if total hours worked is the only thing that matters. Over the past decade or so, they've been rapidly losing ground to law firms that, by not thinking that way, manage to do a better job of producing the kinds of output that clients actually want.