At their positions, rebounding is a fundamental part of being a big man, at any level. Just because they're not athletic doesn't excuse them from the responsibility of rebounding. Rebounding has less to do with athleticism, and much more to do with heart, effort desire and mainly positioning. All a player has to do is seal off the opponent by putting his body in between that of the opponent and the basket. It's that simple. Furthermmore, a smart, seasoned NBA veteran would be somewhat familiar with how and where certain shots will carom off the rim, based on the type of shot taken.
Dennis Rodman was a tremendous athlete, with good jumping ability. However, he didn't rely on that jumping ability to become a rebounding phenom. Instead he did so by using these very, same techniques. KT was once a fine rebounder. He came into the NBA as one of only 3 men to ever lead the NCAA in both scoring and rebounding. He may be older, but the guy does know how to board.
There should never be a scenario where any of the bigs, on this roster, end the game with "0" rebounds, when involved in at least 10-20 minutes of action. That is absolutely inexcusable.