All Unique Metrics (such as frequency) only show on an individual ad level. This is because we aggregate results in your main report view by groups - bundling them by ad name or creative. Since they are being grouped, we cannot combine unique metrics to show averages and therefore they only show in the ad breakdown view. You will need to add these as a metric under the individual ad view.
To do this, you can click into any ad group in your table chart, and add the metric in the right hand pop up!