What size is there that’s a bit smaller than 29″?
We’d have all been happily riding 29ers for years, then 26ers come along, some manufacturers dip their toes in, one or two jump in wholeheartedly. Big arguments ensue on the internet.
A few years later it becomes apparent that people aren’t ready in the massive numbers manufacturers had hoped to make the transition – 26ers are seen as good, and perhaps better for some types of riding, but they aren’t becoming the default choice. Big arguments continue on the internet.
So the manufacturers go back and find a size that’s a bit smaller than 29″ and sell it as giving you the best of both worlds. Although it’s much closer to 29″ than 26″, people try and present them as “27.5” and, having burnt their fingers a bit on 26ers, rather than offering bikes in all sizes, 29ers stop being developed and manufacturers throw their weight fully behind the new wheel size, with 29er increasingly seen as anachronistic, or the preserve of cheap, chainstore BSOs. There are big arguments about it on the internet.