That's because Google, as an American company, needs to ensure it doesn't violate certain trade embargoes, trade export law and other sanctions imposed on specific countries, like Iran.
Google restricts access to some of its business services in certain countries or regions, such as Crimea, Cuba, Iran, North Korea, Sudan, and Syria. If you try to sign in to these services from these countries or regions, the following error appears:
You appear to be signing in from a country where G Suite accounts are not supported.
Certain Google services, such as Gmail, might be available in these countries or regions for personal use, but not for business or education use.
Though some of the Google services are available for personal use in those countries, commercial use is restricted. A cloud would count as commercial use, even if it's only to host your own stuff.
GCP is far from the only cloud to suffer from it and many other services impose this too. The Docker Hub does it too for example.
Here is a list of likely affected territories: https://support.google.com/a/answer/2891389?hl=en
Though some of the Google services are available for personal use in those countries, commercial use is restricted. A cloud would count as commercial use, even if it's only to host your own stuff.GCP is far from the only cloud to suffer from it and many other services impose this too. The Docker Hub does it too for example.