Who said he hasn't been trying to be a leader, as he understands that role? More than once in interviews, Marc has been calling for the team to come together and play as a unit. That players (left unnamed by him) had to sacrifice their individual goals for the goals of the team.
Those are the kind of calls and comments a quiet leader makes. They try to lead by example and ask for others to follow the example. And after every interview where he made those calls, Fiz followed up with an interview saying almost the opposite.