QUOTE
Why isn't synergy ported to platform XYZ?
Probably because the developers don't have access to platform XYZ and/or are unfamiliar with development on XYZ. Also, synergy has inherently non-portable aspects so there's a not insignificant effort involved in porting.
And why would you? Synergy is a util, not a stand-alone program. It even hasn't got it's own graphical desktop... neither has the Xbox.

A TightVNC-client would be cool for the Xbox, though. But then again... Linux can even connect to computers running Terminal Services (also with VNC, by the way), so why bother?