I can actually answer this not as a historian, but as an EOD technician.

To begin, there is something you need to understand which is the concept of a "frag matrix" or "frag sleeve". A frag matrix is a pattern of pre-scoring metal casings of explosive ordnance so that, when the explosive detonates, the metal casing will break along those scored patterns. This results in more consistent and reliable fragmentation patterns, and it is the metal fragments(commonly referred to as shrapnel even though it isnt really) that do the damage in fragmentation grenades. If it werent for this intentional scoring of the frag matrices, grenades could have only a few large pieces going in a few directions rather than lots of little ones going everywhere at once. Also, manufacturing defects in the metal casing might have the case rupture in one large hole rather than shattering, which would do very little.

More than just providing grip, the pineapple pattern acted as a frag matrix. Later grenades that replaced it featured internal frag matrices which were more consistent in performance. If you ever find yourself recovering large pieces of fragmentation grenade casings, you can make out what almost looks like bb-sized impressions in the inner wall of the casing.