I think it's because baseball is already "overloaded" with stats. We are just bombarded with stats when we watch a hitter up on the plate. Batting average, on base percentage, RBI's, runs, home runs, batting average vs. lefties, vs. righties, hitting streaks, ad nauseum. And this doesn't even mention the stats for pitchers. Football stats aren't too bad. We are more willing to accept a convenient stat such as QB rating, cause what else is there for a QB besides completion percentage, yard, TD's, and INT's. The QB rating is a handy stat to quantify how good a quarterback is. BTW, I think your QB rating formula is incomplete. I know that there is a "maximum" rating, and you don't need to be perfect in order to achieve it. The formula you give makes it seem like the maximum only occurs when a QB is perfect.