How is 2 time MLB MVP Roger Maris who also was a complete player and broke the most coveted record in baseball - not in the Hall Of Fame ?
.260 lifetime hitter, only 2 great years, only a bit more than 5000 at bats and despite breaking the Babe's single season record* only had 275 career home runs. Sorry, he doesn't make the cut.
His career stats as a whole weren't that impressive. .260/.345/.476, 127 OPS+, and 38.2 WAR isn't exactly Hall of Fame material. Other players who have had similar stats include Paul O'Neill, Magglio Ordonez, Hanley Ramirez, Troy Glaus, Ryan Zimmerman, and Eric Chavez. I don't see many people arguing that any of those guys should be in the Hall of Fame.
He had roughly 7 good seasons in a 12 year career. 3 or 4 bad ones to start and finish his career. His final stats just don't show much for an entire career. If you made the hall off of 7 years, Don Mattingly would have been voted in a long time ago.
He only played 12 years. He had too short a time period where he was a dominant player - and when he was, he played on a dominant team. He had two great years and two more that were very good, and he was an average to mediocre player for the rest. He never hit .300, he never played a complete season, he had power but was just an average hitter. Never came close to a 200-hit season, had only 850 RBI for his career, just 275 HR, only 1,325 hits, 826 runs scored and had just one Gold Glove.
Because his career stats were otherwise ordinary.
Because injuries ruined his peak.
Because he did not deserve to be voted in.
I guess the voters think Hall of Fame is about a whole career, not just two seasons.