Because they have moved hull volume to the keel line. If you want to keep the overall volume of the hull about the same (as you must or risk bouncing over the waves) then you must take away volume under the deck. In effect the keel line becomes wider, while the deck become narrower. The sides of the hull now don't V-out anymore when going from keel line to deck but rather V-in. Together with the bow wedge (hull sides meeting eachother at the bow) this creates a intersecting line between the two sides of the hull that is raked back on the bow rather then raked forward as is the case with side that V-out towards the deck. Most easy way of producing these hulls is to just have this intersecting line be the bow itself. You could add a piece (triangular) to the bow to give is a straight appearance but this section will both be very thin (breakable), difficult to make, add weight and be pretty much useless as the waterline is further down on the hull. So why make things more complicated, just cut the bow back under an angle and be done with it.

So now the true question becomes why all the new hulls want more volume to be concentrated on the keel line while older boats had rather narrow keel lines. When this is decided then the raked back bow is nothing more then a result.

Wouter