VM instances that only have internal IP addresses (no external IP addresses) can use Private Google Access. They can reach the external IP addresses of Google APIs and services. The source IP address of the packet can be the primary internal IP address of the network interface or an address in an alias IP range that is assigned to the interface. If you disable Private Google Access, the VM instances can no longer reach Google APIs and services; they can only send traffic within the VPC network.
https://cloud.google.com/vpc/docs/configure-private-google-access

Explanation
Instance is alive for no more than 24 hours, Can be pre-empted with a 30 second notice, Discounted Significantly.
Preemptible VM is an instance that you can create and run at a lower cost than normal instances.
However, Compute Engine might stop (pre-empt) these instances if it requires access to those resources for other tasks. Preemptible instances are excess Compute Engine capacity, so their availability varies with usage.
Live at most 24 hours Can be pre-empted with a 30 second notification via API and are Discounted significantly Reference link- https://cloud.google.com/compute/docs/instances/preemptible

Cloud Datastore is the best for semi-structured application data that is used in app engines' applications. Bigtable is best for analytical data with heavy read/write events like AdTech, Financial or IoT data. Cloud Storage is best for structured and unstructured, binary or object data like images, large media files and backups. SQL is best for web frameworks and in existing applications like storing user credentials and customer orders. Cloud Spanner is best for large scale database applications that are larger than two terabytes; for example, for financial trading and e-commerce use cases. As I mentioned at the beginning of the module, depending on your application, you might use one or several of these services to get the job done.

Explanation
Because in the cloud era, users expect more personalization and customization.