Technically, it’s a matter of balance point at the index finger, weight distribution, battery size and hand grip location in respect to the driving plane. But, sometimes the marketing product manager will say, “can we give this next gen family a bit of attitude?” and one result can be a slight tip upward in the driving plane as though the drill is giving you a mad nod. 
Those with a driving plane that is more perpendicular to the handle can look a bit lazy and boring.
The true force exerted when using a drill isn’t with the entire hand, it’s basically just the inner palm between the thumb and forefinger, and drills get twisted into all kinds of weird positions during actual use, so the handle itself becomes something to carry the drill with and something to steady the drill before and after actual use.