I apologize for the lateness of this reason, but it's really a small reason, and it's one that I have explained before some of the other blogs about Absolution. I know this term is sometimes thrown out there, but Hitman is the one game that holds replayability in high regard. Look at Contracts mode, and you see an endless stream of replayability as you can kill anybody you want and any way you want to, with any weapon and any disguise you want to start with.
The main story offers plenty of replayability, mainly due to the choices you have in the way that you play the game. You can do things differently than you did in your first playthrough, and if you scale up the difficulty, you get an entirely different experience than you would each time you play. That's really where the entire entertainment value of Hitman rests, and it has always rested there. Replayability, along with challenge and choice, is one of the pillars of the Hitman experience.
Now, I apologize for the shortness of this reason, but I have a very cool level from Hitman: Contracts that will make up for it, as well as a much longer reason explained in the next Hitman blog. This is Beldingford Manor.