I am sorry Andrew but you are speculating. As an economist your are a great cinematographer.
I will also speculate that their market is not on Cinematography but rather Still Photography, and the Canon 7D (e.g.) still is a great powerful Camera cutting it in many pro areas. Their cinema market is not as big as all these blogs may make us believe, Nikon and Canon know that their competition lies on RED, Blackmagic, Sony Video and Panasonic Video, even ARRIFLEX, companies that have eons of establishment over these two, in the TV AND FILM Industry, so they have to support the community they already know, photography.
All areas of growth have a curve and the tendency is to level once their market has reached a ceiling. Their products are excellent and there lies the reason why many photographers refuse to acquire newer equipment, when their bottom line is still growing. You could go back to 15 years of statistics and will find the same economic conundrum. Its about making the buck, not about having the latest equipment.
I personally still have a powerful 7D that has more lives than a Cat. Makes me money in corporate video. I did buy a 4K BMCC for those "pesky clients that want the latest", but find myself shooting over and over with the trusty 7D and its beautiful image.
Love the Blog, but in this case I believe you are getting in territorial waters.