I don't consider the default behaviour strange. Take a look at this simple shape:
I hope you agree that face A is the very top of the model....made up of the "TOP" layer. You should also agree that face D is the very bottom of the shape.....made up of the "BOTTOM" layer.
What about Face B? and Face C?
Face B is a top layer....and you would expect the Number of Top Layers setting to define exactly the same number of layers as at the very top to get a smooth finish. Similarly, Face C is a bottom layer where you would expect the same number of layers as at the very bottom as per the Bottom layers setting.
Now....my shape is a simple and straight-forward shape with well-defined upward and downward facing "flats". Your shape has a few very thin downward facing "flats"...if you consider a sloping face to be a "staircase"....and the same rules that apply to my shape are being applied to yours. And using two profiles is the natural way to stop the "accidental" creation of bottom layers where you don't really want them.
btw.....other changes would also achieve the same result (eg more perimeters, thinner layers, smaller nozzle, etc)