Your data set is defined as individual point with a long and lat that get plotted on a map
When plotted as Auto they are Circles that you change the size with your count measure
Switching to "filled map" will plot the same points - they are not shapes (areas) - and you are filling the "shape" -
the Shape defined this way will not expand based on your measure
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But why aren't they shapes? How can I make it so that the size changes even in map mode?
You would need a shape file (spatial) for them to have a shape (define a polygon) they are a point on the map one combination of Lon/Lat