The problem is not the variance in results (which everyone seems plenty in the game), but the way *expected* results can be rather accurately derived from in-game attributes, when those are the true drivers of the simulation engine (which they are in The Show). Inferring ability to perform in future from past performance (stats, memory, etc.) or by subjective impression (e.g., scouting) is entirely different from looking directly at the true ability.
For statisticians, those are basically the differences between sample mean (something like scouting), population mean (perhaps stats like WAR), vs "true" population mean (attributes).
Basically scouting and advanced stats like WAR are trying very hard, from different perspectives, to estimate what that "true" talent level is for a player. The game, on the other hand, is actually giving us THE truth.
And a whole a lot of people enjoy doing scouting and calculating WARs. No need to do so in a game that provides the truth upfront.

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