Because this it's (parce c'est comme ça )why
From what I see in 3D view PartDesign could do it as well. The mistake PartDesign seems to make is to erroneously assume some instances were not intersecting - which in fact they do:
Nice solution. Never used Facebinders till now. It could solve some problem I had in other project. Do you think would it be possible to get straight corners instead of round?
FreeCAD crashes if I try to do the sweep including the circle. Based on GlouGlou's model, I did the following:
I think so. Just replace the revolve with 2 extruded facebinders. Extrude them past each other, then take the common.