WHY AREN'T MORE ADV TIRES RADIAL?

[Spuddy]

While anticipating replacement tires for my '13 Stelvio NTX, I've noticed some manufactures don't have radial dual sport tires, or only radials at the rear.  Could it be stiffer sidewalls are more predictable on gravel or dirt?

[mtiberio]

or better at rim protectors. perhaps narrow tires are better in the dirt.