Mathematically speaking I am not sure why they are not all like this. It means one pedestrian phase in the sequence (so sequence is quicker) and everyone is a winner. There is one near me it is a joy to go diagonal!
It's only better if the intersection has high, consistent pedestrian traffic. Unfortunately, many cities aren't built to be pedestrian friendly so those criteria are rarely met outside of busy cities, downtowns, and college towns.