It’s all about risk. If you have a simple enough system, you might be able to hide it behind an abstraction layer that adequately contains the possible effects of change.

But many interesting useful real-world systems are difficult to contain within a perfect black box. Abstractions are leaky. An API gateway, for example, cannot hide increased latency in the backend.

People accountable for technology have learned, through years of pain, not to trust changes that claim to be purely technical with no possible impact on business functionality. Hence testing, approval and cost.