How do you know why project zero exists?
It says on their website:
> Project Zero's mission is to make 0-day hard. We often work with other companies to find and report security vulnerabilities, with the ultimate goal of advocating for structural security improvements in popular systems to help protect people everywhere.
Why they say they exist and why they actually exist are two different things entirely. There’s not a single corporation (except maybe B corps) that spends money like this without a competitive agenda. Off the top of my head are a couple obvious reasons for PZ: to help with recruitment, to give the company some good press, to make their competitors look bad, or to fix their own Android exploits before anyone else knows.
I don't think you quite understand why Google Project Zero team exists in the first place. Their job is to make the world a more secure place. They seem choose whatever they want to work on to maximize their impact on the world –ranging from Intel processors to iPhones to some first party technologies like Chrome.