Because it's not a document converter, it's not part of the UI, and it has nothing to do with Microsoft. That's just what UIMXDC happens to stand for.
In fact, this class only exist in order to implement one of the methods defined in the IPrintOemUIMXDC interface. Since the basic piece of software here is an XPS driver called "Golden Jet" the name goes: XPS Driver, Golden Jet, the part which implements that stupid UIMXDC thing.
IPrintOemUIMXDC is an interface exported by a Unidrv UI plugin which provides three methods that MXDC uses to determine how to perform certain actions when converting a GDI print job to an XPS document. In this case I need to control the image compression (i.e. disable it).
So the name didn't arise as capriciously as it might seem at first. It still sucks though.
could have put that in the op and saved us the time of humoring you