What??? Have you ever touched a knee pad, or an elbow wrap, taped fingers, etc. that allows an opponent to penetrate/grip them like regular skin? Besides, there isn't a lot of gripping with the fingers by one wrestler on another wrestler. Most of the gripping is by the hand, and is either on one or both of the wrists, which are often sweaty as hell (and thus somewhat difficult to grip as they are slippery), or on an ankle, which is covered by a shoe (which is somewhat different than gripping skin).
Rule 1 (Mats, Uniforms and Equipment), Section 7 (Special Equipment), Art. 1 (Description)
Special equipment is defined as any equipment worn that is not required by rule and includes, but is not limited to, hair coverings, face masks, pads and braces. Special equipment that does not allow normal movement of the joints, prevents one’s opponent from applying normal holds or is excessively loose-fitting shall be barred. All legal special equipment that is hard and/or abrasive shall be covered and properly padded with high-density foam.