Earlier quoted context omitted.
How so? The soldiers don't need to carry the "nice to have" items and if it get struck it's not such a big deal.
1. Being OK to lose doesn't fix the problem of it being noisy. 2. There aren't many truly "It's OK to lose it" items, as they'd all have been lost by overburdened soldiers already.
Noise is a different issue of course, but the article mentions it only for the walking "big dog" mules, not for wheeled ones. And if the mule only carries stuff that's not immediately essential, it doesn't have to stay close to the squad. If it can follow them autonomously (which is probably a requirement anyway), it could trail them at some distance.