1. Because they'd probably have to hire several hundred humans and give them benefits. It's much cheaper just to trust the robots.
2. Unlike a small hosting company, Google is so big it will suffer essentially no financial consequences if their robots make a wrong decision for credit card customers a few times per month.
So there is no cost to Google for leaving the system as is, and a high cost for your solution. The decision is a no-brainer from their point of view.