I think it's simply that his market demands this sort of tire. And I think that there is a rather big demand for fat, supple 29er tires; I predict these will be best sellers.
I both agree and disagree with Jan's views on wheel size, tire width, and handling, meaning that "optimum" in reference to handling is a word that has to accommodate so many different preferences. I can certainly tell the difference between a 26er with light 55 mm tires, and my Matthews with 29 1/2" tall, 61mm actually wide tires; but given that these last seem to me to handle sand (and small bumps too) better (Jan disagrees), I choose the less nimble handling larger wheels, and find that these are really not bad at all.
On the other extreme: very light, 24 3/4" (559 X 29mm) wheels on my Riv Roads: is the handling of these wheels less "optimum" than 650B X 42? Perhaps to some riders; perhaps even generally, in some theoretical way; but in my own experience over very many different bikes over almost 50 years of assembling or modifying (and certainly buying and flipping) my own, they set a benchmark for good handling -- Grant designed the frames to accommodate such light and short wheels.