Well, of course from a financial standpoint of view one cannot order a batch of hundreds of forks and frames to be built and sold with a sensible revenue&profit. Investment in such a new wheel size could be done only by well-off companies, together to say the least. Let's say Fox partnering with several main stream frame developers and tyre & wheels manufacturers with after market parts. With 29ers it was step by step in 2001 with Gary Fisher and it took almost twenty years to get them right, to get them 29er specific parts, gear ratios etc. All this would have to be done at once with many companies in "complot" to bring it all and done right in one year instead of twenty. We are not turtles or whales, who can wait for dozens of years.
As for 29+ it is what it begins to be shown with 27,5+ - tyres over 3" tend to be too bouncy to provide a reasonable ride over light AM and XC terrain. People, when faced with a choice 27,5"x 3,25" would rather use a 29x2,6" on the same frame on longer rides and consequently 27,5+ begins too shrink like 27,5", which were invented when 29ers were still improperly designed. It is generalization to be sure and one can find many examples to contradict this.
