In the allegation, Apple is not the monopoly... it's the PUBLISHERS who, by colluding together, that form a monopoly, and then abused their market power. Allegedly. In the DoJ's case, to put in simpler terms, Apple is being accused of at least being the bank robber's getaway car-driver, or even the mastermind. Not the actual robbers, but still a part of it. As I've read it, that's the case they're basically trying to make.