Why should they remove them from the game?

Nin tai *ion have a big influence if your enemy has a ton of damage reduction stacked. They counter damage reduction stat effect bonus to def and res. If your target has 3k damage reduction and you own 2500 nin *ion lets say you see a significative increase of your damage in comparison with somebody that owns 0 *ion. If your target has 0 damage reduction you do not see any difference.