No reason was given for the delay.
Hitman seems like it will be a gosh darn awesome game. The title will be launching episodically over the course of this year, and a disc release was slated for the end of this year (itself delayed from originally launching alongside the first episode)- however, it has now been delayed into 2017.
We don’t have any reason for the delay yet- this may indicate that the final episode of this season of Hitman will bleed over into next year too, since the general understanding has been that Square will try to release a full version once the season is complete.
But that all remains speculation. For now, if you are one of the people who were looking at getting into Hitman, nothing has changed- you can still start playing the game from tomorrow onwards. If, however, you were waiting for the disc release? Well, you will be waiting a little longer.