[sailingfool]

Big aft ends can provide space for a big aft cabin and perhaps room for good seating, if not a a couch in the cockpit, but contribute nothing positive to any aspect of sailing performance and tend to make a boat even less suitable for offshore use. Buyers of these boats want to cruise the gang in comfort for their afternoon sail, and for that, such designs make sense.
In terms of useable space, it''s all an illusion anyway, because the stern of a sailboat is generally unliveable, other than perhaps being a good place to kennel a pet. The average quarterberth is the least habititable spot in a boat: make the area real wide, tucked under the cockpit and put a door on it, and what you have is a nicely finished maximum security cell.
All boats are an accumulation of tradeoffs - big sterns provide daysailing comfort at the cost of sea-kindliness and offshore capability.