Total Zone is based on knowing hit locations. When a fielder fails to make a play it is normally a hit or error (or sometimes a fielders choice). Often you cannot tell who to "charge" with the hit. Maybe it was a line drive that nobody had a real chance at, maybe it fell just in front of an outfielder, maybe it was a grounder hit between short and third. Total Zone, if it does not have the exact location and type of hit, makes estimates. I think that is a reasonable thing to do. And I think that Total Zone does a good job of estimating the impact of fielding.