Apparently, your set analysis forces the single value-dimension 'LocationQuality' to go into hiding. Check it out: eliminate the LocationQuality dimension. Nothing will change.
And this only happens in graphs, not in table charts. If you change the chart type to Straight Table, two dimension columns will appear, and clicking on the value will select values in both dimensions.
I think this is default behavior. You can try turning this series of charts into a Trellis setup (with LocationQuality as Trellis dimension). That will allow you to select the two dimension values.