They pay a team to embarrass competitors. The technical aspect is a small part of what is happening here.
Competitors should be embarrassed when it concerns security flaws. It's one of the best ways to generate media buzz and inform customers about the flaws, and also their consequences.
So you don't view this as Apple getting free whitehat testing and a chance to not get hacked? I think there are two viewpoints you could take here and I think the truth is directly in the middle.
I wish my competitors "embarrassed" me by helping to improve my software for free.
There are many possible motivations for Project Zero, and the reality is that more than one is likely responsible for the inception and ongoing sponsorship of the team's membership and activity.