Answer: Because none of our cameras have the sensor of the D800. We will never have a camera as good as the D800.
You really think so? That would imply Canon has decided their current range of sensors is perfect and no improvement is possible or necessary. That seems highly unlikely to me. Canon's sensors were way ahead of anything Nikon had for years, so you could have said the same thing about Nikon until their recent models came out.
Nikon may have leapfrogged Canon for now and caught them napping, but I doubt the Canon execs are saying, Oh well, they beat us - time to throw in the towel and give up our multi-million dollar business. The apparent sightings of a high MP Canon in the field, supposedly sporting advanced new sensor technology, would seem to bear that out.