To put it simply, because the people buying football video games are not NFL quarterbacks"
BS...
The reason is they don't know how. Has zero to do with who's playing the game.
This isn't just with line blocking either, but a lot of areas in the game. That's why more times than not a "feature" is implemented to do nothing more than cover up bad AI programming.
The real question is will we ever get a game that actually moves the genre forward.

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