I imagine they want to reduce the amount of credits one can collect with additional copies of Common and Uncommon cards, but this could also be achieved by simply reducing the amount of credits they provide (and cost, spending 100 Credits per Trainer card does not feel great)
This drove up the cards price, as looping two copies of We Know the Way is effectively the decks win condition
Source: Magic: The Gathering/YouTube Magic: The Gathering Arena Released September 27, 2018 ESRB T for Teen // Blood and Gore, Mild Fantasy Violence Developer(s) Wizards of the Coast, Wizards Digital Games Studios Publisher(s) Wizards of the Coast Engine Unity Multiplayer Online Multiplayer Franchise Magic: The Gathering Platform(s) PC, Android, iOS Genre(s) Digital Card Game OpenCritic Rating Strong
The new aura roles are a token (and an enchantment) so they can be bargained away
Plus, with local Aussie shipping, you won't be left waiting weeks for your cards to arrive