Google certainly has more monetary resources. But in my experience large companies like Google are the ones that can't afford to do something like this. The logistical benefits of white-boarding interviews and the accountability gains are much more important to large companies. This interview process was for a smaller company.

But you're absolutely correct that the more time-consuming the interview process is for the candidate, the more likely they'll interview somewhere else. In fact, that's exactly what I did: I received an offer partway through this git-based interview process, and the offer was good enough that I didn't see value in completing it.