This makes a lot of sense to me in the way you have said it.

The department probably exists in the first place as a result of an internal political struggle and compromise - with some decision-makers wanting Google to be genuinely more ethical, and others wanting to avoid any genuine oversight.

As a result, you have this bodge solution where the department gets to exist (helped by the PR benefit as mentioned elsewhere), but not to act independently. Anyone in the department offering genuine oversight is at risk of being forced out.