The coach said he could no longer leave new recruit Tom Duffy unrewarded for his promising start to life at the Broncos, sensationally relegating Mam to the bench for Saturday's derby against Gold Coast.
Rated the club's long-term five-eighth, Mam has paid the price for Sunday's abysmal loss to last-placed St George Illawarra, and the Broncos' underwhelming start to their premiership defence.
"It's about being successful each weekend and we haven't hit the mark there over the last month," said Maguire, whose side are on a four-game losing streak with a 5-7 record.
Maguire's selection call was purely based on form, unrelated to Mam's training attitude or off-field circumstances.
"You make decisions around what you feel is right. Obviously Ezra's been going through a bit with his game and then Tom Duffy's been playing well," he said.
"I've always been one to, when someone's performing well, give them an opportunity. This is just a moment in time that Ezra's going through. He's gone back and worked hard at his game.
"Every player may go through that or will go through that at some stage. It's about responding."
Mam is no guarantee to make it onto the field against the Titans, so may not have the chance to reaffirm his Origin credentials before teams are picked for game two.
The 23-year-old is uncapped at Origin level, but was Queensland's back-up playmaker on the bench for their tight game-one loss.
Despite the ramifications of his axing, Mam has taken Maguire's decision in his stride.
"He's (all) right, he understands," Maguire said.
"I'm pretty transparent about what is expected and to be honest, the players are themselves. He knows himself as well, which is a good thing.
"It's about just going back, getting your practice in and getting to the game that we know Ez can play. He's a quality player ... he's on the bench for a reason. We'll see how the game plays out."
It comes as Gold Coast promote former Origin prop Moeaki Fotuaika to co-captain alongside Tino Fa'asuamaleaui, who is having a quiet season by his standards.
But first-year coach Josh Hannay's mid-season change was more about now having had the chance to observe the group dynamics and appreciate Fotuaika's leadership presence.
"Leadership is one of those things, it's not a gift or a reward, and you don't just hand it out on a hunch. You've got to actually see people lead," Hannay, who consulted Fa'asuamaleaui before making the call, said.
"He was like, 'What's taken you so long to make him co-captain?' He respects that guy, understands what the club means to him."
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