Because the goal is to minimize contact in the fore arm. "Glass" won't stiffen it enough to counteract wood movement either. (Actual fiberglass hasn't been used for many decades. What we call "glass bedding" is nothing more nor less than epoxy, usually with colloidal silica or metallic stiffeners added.)
One thing I discovered with rifles sporting barrel band swivels is that one needs to sight in with the sling hanging in place like it would be in the field as POI can shift a bit from when it was sighted in sans sling. That or leave the sling off when hunting and resort to its use when both hands are needed to drag a deer carcass (or your own carcass) out of the woods.
"You can lead a man to logic, but you cannot make him think." Joe Harz
"Always certain, often right." Keith McCafferty
| 
