The question is what’s reworking the surface? Plate techtonics? Nope, it’s geologically dead (well... see below). Constant bombardment? Nope; those are the craters that are missing. Erosion? Nope; not much atmosphere.
The real answer is that it’s not really so dead techtonically. While any rock material would’ve cooled off by now, it may harbor vast oceans underneath an icy surface.
The lack of craters is the result of a lack of impacting matter.
Pluto is beyond the asteroid belt and source of the zillions of matter that can impact