Why isn't Artis Gilmore in the hall of fame?

This has been bugging the hell out of me. Artis Gilmore was a dominant NBA player who, to this day, holds the record for accuracy in shooting. He holds the NCAA record for rebounds/game at 22.7. almost 23 boards a game! There's tons of players with lesser stats in ahead of him. It makes no sense. And as far as him playing in the ABA, this is the BASKETBALL hall of fame that's being discussed, not the NBA HOF. It bums me all the way out. On top (ha!) of everything else, he was a strong as an ox and had one of the best afros to ever grace a basketball court. Artis is being robbed and I can't stand it!

here's his career numbers. he stacks up against anyone.
http://www.basketball-reference.com/players/g/gilmoar01.html