I think we may be talking at cross purposes here. My point is that the suggestion that 29" is the same as 28" as 700c and these sizes have been around for a long time, or that it is all just the industry creating new markets from old, does not address some very valid reasons for their developmental use.

You can look at 29r/700c use off road along two pathways - mtb or cyclocross, and see why they developed two very different wheelset and tire designs.

First cyclocross.
Road oriented off road riding with a lot of crossover in components. The desire to use 700c wheels with moderate tread and size. The use for racing XC, and arbitrary rules, limits the forward development in size or aggressive tread. Specific use dictates and limits design expansion. So you have road oriented off road bikes with light fast 700c tires that are moderately wide.

Perhaps Graham can comment as to whether the Finnish riders were seeking the ability to ride in snow with road bikes or had a more cyclocross orientation. I don't know about that.

Mtb took a different path.
From its inception, as well documented by repack rider (aka Charlie) one major purpose was riding downhill. The first klunkers were cobbled together to accomplish this goal. The first semi/commercially built bikes followed this idea and were not just road oriented bikes with smaller tires. Everything was beefed up to survive downhill abuse. To go larger tire at that point would have been problematic for several reasons: The wheels were not strong enough, the gearing was inadequate and the envelope for 26" design hadn't been achieved yet. 26" design was still growing it ability.

Rather, in the 1980's 26" rigid design moved towards its apex in capability. Then the suspension fork extended that capability and eventually full suspension evolved which allowed the rider to tackle terrain more extreme than before.

No longer limited by strength, lightness or suspension; larger wheel size, and its ability to roll over obstacles easier, became the limiting factor. The 29r evolved to meet that now apparent deficit. Same sizes nominally, but two very different performance objectives: light/fast vs strong/aggressive tread. Put a modern cyclocross wheelset next to a modern DH 29r wheelset and you see what happened there.

Coincidentally, braking and gearing also plays a part in 29r use. Once you have the suspension and wheel size to bomb technical downhill you are limited by your braking ability. Canti - V - mechanical disc - 160-180 rotor - hydro disc - quad piston... And with full suspension, larger wheelsets and the bulkier bikes to support them you need lower gearing to ride back uphill.

Some may think they just slapped some 700c tires on a mountain bike but I see the evolutionary process at work throughout.