Iggy was a more meaningful player that series than Curry was -- if "only" by virtue of having to show up all 7 games and guard the best player on the floor in addition to contributing a not-insignificant amount on the offensive end.
I think if LeBron had given another unreal performance he would have won the award. He didn't (although that's strange to type, given the fact that he "only" went 32-18-8), and the Cavaliers couldn't come up with a win despite the blatant home court advantage they were given by the referees, particularly apparent at the free throw line and what was being called in the second quarter on the Warriors compared to what CLE were getting away with on offense.
Anyway, 25-5-5 with 0 turnovers, the highest assist percentage on the team despite not being a point guard, and being the best perimeter defender on a team that rode perimeter D to a title at the expense of their best defensive big? Award is justified to me.