Because the game doesn't support 3440x1440 resolution in a way I find appealing or want to play. I also find the PC port lacking in ways beyond the cloth. It is also hard to play this PC version of an AC game when I remember past AC games running wonderfully on the PC with all the options of the day incorporated. It is disappointing.
So I also bought the game on a platform that it was obviously designed for, and I'll play it there.
Who cares.
2008-2011 AC games on PC were not noticeably improved on PC hence why they were very easy on the hardware, since ACIII PC versions have incorporated high-end features.
It seems you'd rather those improvements never have made it into the PC version so they would run as easily as past AssCreed games.