Because controls ensures that people stay honest. I worked on a treasury system for a significant (not federal) organization. By design, I couldn’t even see aspects of the system directly.

When you give people unfettered access to sensitive information, your risk is exponentially greater. Those people can be compromised, tricked, engage in fraud, be victims or frauds, etc.

Worse, because access is unfettered and controls bypassed, you may never know.