It's because baseball writers, far more so than sportswriters in any other sport (though sports journalism is a joke, generally speaking), are completely up their ass about the "Americana" and the history of the game. For fuck's sake, Abner Doubleday is still regarded as the father of baseball despite the fact that it isn't true
. The same holds true for the Hall of Fame: The BBWAA treats it as a sacred cathedral, instead of "historical museum of the best who played the game," which is why you get assholes who turn in blank ballots because they don't want too many people in there, the pricks like Joe Morgan who actively campaign against people at their position getting in (like Ryne Sandberg), and so on and so forth.
Were you one of the very best to play the game at your position for a prolonged period of time (or, in Craig Biggio's case, were you an absolute monster at three drastically different positions
for a prolonged period of time)? Congratulations, you're in the Hall of Fame.