It's just due diligence. Think of what you have access to if you have "god mode" on corporate chat: HR, the CFO's DMs, private messages between other coworkers, and so on. Most won't fall for this temptation, but even those with strong anti-spying morals can be weakened by circumstances. Best to remove the temptation by design.

Because someone else's devops can't use it against you institutionally. Nor is going to insist on having an opinion on things that they're unaffected by.

This isn't a slam at devops, it's about the need for institutional information hiding; not everyone needs to know about and weigh in on every decision being made.

We structure our company similarly. With effort DevOps is god on everything except HR, Sales, Finance, Chat, and C-level management which are operated with 3rd party services controlled by the individual departments and "owned/managed" by the C-suite.

Low maturity risk management functions.