Earlier quoted context omitted.
Especially when Amazon is making moves into insurance and pharmacy spaces
The difference is Amazon won't use confidential AWS data to drive their other verticals. Google's very business model is selling their users to their customers.
That being said, and with 15 years of adtech of experience, I guarantee that there's absolutely no usage of business customers' first party data by Google's adtech system. While companies can use it to match and target their users, they have to do explicitly with lots of restrictions and protocols and it's only become more limited with new privacy regulations.