I am thinking due to reading posts from other websites that maybe this is so because of "no more hot clocks". The alleged benches as supplied are supposedly in line with no hot clocks (but increase in SPs). If hot clocks were still employed then those number may have been a lot higher (hypothetical guess). But that would mean, the TDP would go up and probably play havoc with other aspects of the GK104 (including yield).
They could have doubled SPs but allowed for hot clocks or they could have as rumors suggest tripled SPs but done away with hot clocks. But maybe architecturally they decided no more hot clocks as they can pack more into an area w/o having to resolve to hot clocks with 28nm?
At any rate I will await for more substantiated benchies etc than a Chinese website