Because Helm of Obediences ability only stops milling once it has either milled X cards or a creature, if you have a replacement effect in play that exiles cards when they go to the graveyard, the Helm never sees either of its conditions met, and it just mills the entire library
Take Elite Trainer boxes as an example
Raiders' Karve Our only charting common is this 3-drop, 3 crew 4/4 that will ramp the top land of your library to the battlefield tapped, which is good advantage over time and adds mana ramping to non-Green decks since the Karve is colorless
Elgaud Shieldmate gives both paired creatures hexproof while Druid's Familiar gives both creatures +2/+2
Many players prefer collecting cards in their native language for personal preference and easier rules understanding
Giving those tokens a +1/+1 bonus counts for a sizeable advantage when you have five, ten, or even fifteen Zombies on the battlefield