Oh Gosh, This is Going to Get Misinterpretd
ABS in the "Adventure" motorcycle market is, to an extent, a marketing object. The bikes are meant to go well down the road, and on unfinished, less-maintained surfaces, with a level of parity.
It sounds like there is an implied assumption on the consumers' part that the ABS on these bikes is intended only for that road portion of the travel; the reason why not having a deactivation procedure (or even a less involved one) can be a mark against that particular bike in the eyes of a customer who wants more dirt bias.
The people who buy a given bike, who intend to use it for something beyond its intended purpose, but who fail to consider the need to alter it to suit their desire, are probably not going to consider the ABS-dirt relationship either.
My riding shoes are Adidas. Boom