Because eyes are actually a defining feature of a person.
Faces have a lot of defining features. Hiding the eyes would sometimes suffice to hide the identity of a person.
You can’t possibly think that the protected person is someone else based on their mouth and nose, would you? You still won’t have high confidence.
On top of that, audience thinks it’s more believable that the person is real. Vs blurring the whole face, it could be Donald trump or the show producer behind the blur for all we know
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