Access methods to services in Google production infrastructure

[mountaincode2]

I am reaching out with a query in relation to the following page:

https://cloud.google.com/vpc/docs/private-access-options

The doc says:

> The access methods are different for services in VPC networks compared to services in Google's production infrastructure. The former use peering or Private Service Connect; the latter use Private Google Access or Private Service Connect.

My query is: what is the Google's production infrastructure. And why is the access method different for Google's production infrastructure.