Because cross-team partnerships are part of the visibility cost management strategy.
https://wa.aws.amazon.com/wat.question.COST_1.en.html

Implied rules Every VPC network has two implied firewall rules. These rules exist, but are not shown in the Cloud Console:
Implied allow egress rule. An egress rule whose action is allow, destination is 0.0.0.0/0, and priority is the lowest possible (65535) lets any instance send traffic to any destination, except for traffic blocked by Google Cloud. A higher priority firewall rule may restrict outbound access. Internet access is allowed if no other firewall rules deny outbound traffic and if the instance has an external IP address or uses a Cloud NAT instance. For more information, see Internet access requirements.

Reference link- https://cloud.google.com/vpc/docs/firewalls

Scalability. When your apps require additional compute resources, autoscaled MIGs can automatically grow the number of instances in the group to meet demand. If demand drops, autoscaled MIGs can automatically shrink to reduce your costs

https://cloud.google.com/compute/docs/instance-groups

Compute Engine lets you purchase committed use contracts in return for deeply discounted prices for VM usage. These discounts are referred to as committed use discounts. Committed use discounts are ideal for workloads with predictable resource needs. When you purchase a committed use contract, you purchase Compute Engine resources-such as vCPUs, memory, GPUs, local SSDs, and sole-tenant nodes-at a discounted price in return for committing to paying for those resources for 1 year or 3 years. The discount is up to 57% for most resources like machine types or GPUs. The discount is up to 70% for memory-optimized machine types.