[Jensson]

Amazon and Microsoft uses AWS and Azure themselves. Google doesn't use GCP, the service you buy is not the service Google engineers use internally. This both means that GCP cannot bill the rest of Google to inflate their own numbers and that GCP likely are less battle tested since they don't have a huge internal customer.

[tonyedgecombe]

Also there seems to be a widespread perception among developers that Google will drop services on a whim. Whether it's true or not that has to have an impact on people signing up to their services.