I'm surprised nobody has brought up 650b. It's been a trend in the MTB scene for a while now too, as well as in commuting and city bikes for many years (especially in Europe)
I don't put much faith in the bike industry conspiracy thing for 29er MTB. It started as a fringe thing and the bike industry RESPONDED to what the "People" wanted. Same goes with 650b, more are starting to pop up. Actually the same reason 26" tires took hold as the first MTB tire in the early 80's....folks were converting their old 26" cruiser bikes to be more capable off road, and a few companies responded with more dirt friendly 26" tires. It took off as the standard for many years, and just recently have other tire options become more available...not because the evil bike industry wants to suck you dry, but because people want to have bikes that fit them in size, riding style, etc...and not everyone is built the same. Now, instead of one standard MTB tire size, there are three.
I think options are great. 26" is not going anywhere any time soon. It's the most popular size of tire world wide.
Anyways, I would think 650b is a more practical option for commuting than 29er. That's my personal opinion.
Bike shops respond to what people ask for. If 9 out of 10 customers ask for 29ers, that's what you're going to see on the sales floor. If it makes more sense profit-wise to manufacture 29er bikes because 9 of 10 customers are asking for them, that's what the "big" companies are going to carry. If you don't like it, buy one of the millions of 26", 700c, 650b, 650a, 650c, 20", 24"...etc...bikes that are still available