The main reason is that whatever Grapploct does, Sirfetch'd does better, and in turn, Conkeldurr does better than both. So, abilities first. Conkeldurr gets 3 solid abilities. These breing Iron Fist, Sheer Force and Guts. These abilities work especially well for many Conkeldurr sets like Flame Orb and Elemental Punches sets. As well as Life Orb. Grapploct only gets Technician which is barely usable mostly because of its movepool. Now Stats. Grapploct has 80/118/90/70/80/42. Conkeldurr has 105/140/95/55/65/45. So, Conkeldurr is superior in every stat except Special Attack and Special Defense, only the second of which matters. Finally is the movepool. Grapploct has access to good moves such as Bulk Up, Close Combat, Brutal Swing for Technician, Drain Punch and Sucker Punch to help it. Conkeldurr gets Facade, Mach Puch, Elemental Punches, Drain Punch, Close Combat and many other moves at its disposal. So, to conclude, Grapploct is in PU because it's outclassed in every way by other Fighting types that serve the same purpose such as Conkeldurr.