This image already feels sharp because of the lighting and the subject.
There are countless visual cues: edges which establish a sense of depth and texture.
Only moderate sharpening is required: too much will result in a contrived appearance.
This image looks soft, even though it contains a lot of detail.
There are fewer edges, no strong transitions.
Some photographers would say that the image is lacking in "local contrast"".
More sharpening is required for an impression of sharpness.