No, you're not missing anything. By default, Excel applies data labels to each data point individually, so you have to change the label settings for each data series separately. However, there is a workaround that allows you to format all data labels for all data series at once.

Here are the steps:

1. Select the chart and go to the "Format" tab in the ribbon.
2. Click on "Format Selection" in the "Current Selection" group.
3. In the "Format Data Labels" dialog box, select "Series Name" instead of "Value".
4. Click on "Alignment" and choose "Rotate all text 90 degrees".
5. Click "Close" to apply the changes.

This should format all data labels for all data series at once. Keep in mind that this will also change the labels for any future data series you add to the chart. If you want to revert back to the default settings, simply repeat the steps and choose "Value" instead of "Series Name" and "Horizontal" instead of "Rotate all text 90 degrees".