That is a very interesting counterpoint! I guess I agree with you if the choice has to be between {Google, Amazon} or "only Amazon". But I'm advocating for the third choice, where we continue (or go back) to running our own infrastructure.
I'm fairly sure that's the main reason why AWS and GCP are so popular, not some nefarious marketing conspiracy.
EDIT: I guess you could advocate against Google, Amazon, Microsoft in general for anti monopoly purposes, but that's not the same as using a cloud provider. Granted, those three are the top three offerings.