But it does fix the problem of it becoming an attractive target for the enemy. If the mule carries special weaponry, taking it out is attractive to the enemy. If it only carries stuff that the squad isn't going to need in the current engagement, there's no reason for the enemy to focus on it.

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.