My guess is that it’s designed for that. Looking at the picture on the blog post, it seems like the external joint fits on to a clip built into the trousers. My guess is also that it’s so you can charge the unit without leaving the trousers lying around. Also, if my guess is correct, it allows for swapping out units on longer hikes, when the battery runs low.
Also, if they are renting them, they need to be thoroughly cleaned in between*. So it makes sense to have the motor bits easily swapped out between rentable trousers.
*Er. I hope.
