Because they needed three hours to fill, and the KOTR wasn't much of a PPV draw the last time they did it (which just had the finals on PPV), or when it was just a one-night tourney.
Holy shit, KING REGAL! I wasn't expecting that, but after Regal's had good matches since facing Orton, I have no major issue with Regal making a regular in-ring return. Plus, they got the Regal Stretch over as a killer finisher for the first time...ever in WWE. Excellent stuff, aside from the tourney matches being too short.