The Finger Pointee/Half-Assed, Lame, Hand-Grip Mistake

This topic came up in one of my numerous reality vs. fantasy debates i have on discussion boards. It took me mere minutes to find a sample on a martial arts webpage. I always worry about instructors and then their students doing joint locks and limb catches with the showy, prissy, dangerous mistake of, when doing said joint locks and their related takedowns, using their pointer-finger as a directional guide and then barely grabbing the limb they are manipulating. See picture. Look at grab.

This is a sample of someone proud enough to use this photo on his webpage. Look at the pointee finger. Look at the lame, three-finger grip on...a KNIFE-BEARING LIMB!!!! (You might call this thumb-up pose another version of my coined phrase "Knife Cancer Grip.")
Why? Why? Why? What sense does this make? Real people fighting need ALL their fingers involved in a fight. especially against a knife.