Hi, Welcome to Sailnet!
It's largely an aesthetic preference, although a canoe stern arguably offers an advantage in severe weather conditions off-shore, with large following seas.
A down-side is that, for a given length, the hull will lose some interior volume. This is why canoe-sterns are even less common on smaller designs - they simply can't afford to give-up that interior space. Of course, there are some exceptions (Quickstep 24 comes to mind).
A while back, we had a good discussion about canoe sterns here