Global touring is a niche, with very specific needs. Even if the general trend is the increase of the size of the wheels, there might specific reasons for a heavy duty touring bike to prefer smaller wheels, like resistance to higher loads or wider worldwide availability of tires. For this specific application, the general trend is less relevant that the needs for this use case.
Note that on max allowed weight, the bikes you linked are on the high side, but are not record breaking - 160kg. It's possible to find 700c/29" touring bikes with higher max allowed weight - like the Decathlon Riverside 900 touring, rated at 170kg, so that wouldn't mean it's a condition to tolerate higher loads.
As other answers pointed out, availability of 26" shouldn't be an issue, but I would think that unless you fit into a niche where 26" remains relevant, 700c/29" might be a better choice: it's more comfortable, more efficient and more common in some parts of the world. The fact that it is more common available also means that you'll have more choice in tires and tubes.
Note that if your goal is real touring in remote, there are other considerations. The 26er you linked has for example very exotic brakes (Magura Hydraulic rim brakes, and for many tourers, that would be a no go, as it would be impossible to service them in remote areas).