Why so big a wheel? The Unicycling Society of American says:
"For riding outdoors on the street, you can use a 20” freestyle unicycle, or you can use a unicycle with a somewhat larger wheel, say, 24” to 29”. The larger the wheel, the faster and farther you can ride. Beginners will find it easiest to start on a unicycle with a 20” to 24” wheel. Smaller children may need to start on a 16” wheel." (emphasis added)Unicycle.com says they sell 5000 a year in the US and another 5000 outside the US and their goal is to reach 1% of the population. The link has the owner pitching to funders about his unicycle business. He estimates about 1 million unicycles in the US.