After 2 ABs, guys are often hitting 1.000. Obviously, we should extrapolate that out for an entire season, no? Fielding stats are even more so. Every guy will get to 95% of the same balls hit to them. That means the difference lays in those final 5% of hit balls. And it takes time to gather enough of that "5%" to say anything meaningful about the player. You remove outliers (say, a guy tripping, getting an unusually bad jump, or getting lucky by being shifted badly on an oddly hit ball) by waiting until you have more data. Outliers have far less impact if an odd play counts for .1% instead of 1% of the gathered data. In the meantime, those same outliers can drastically skew data one way or the other in SSS. It's Statistics 101 stuff.