Well I know very little about suspension but in a simple hypothetical example:
- with McPherson you can have the control arm horizontal in the uppermost position and make it half the width of the car. (since it's on the bottom). That gives massive travel (with massive camber change) and there is still a lot of space between the wheels (for engine, cooling etc.)
- if you want to have as much travel with double wishbone the upper wishbone needs to extend also half the width of the car. Even if the vertical distance between the two wishbones is low it will eat up space between the wheels. (Angling the dampers inwards to give extra space for the upper wishbone also eats space.)

Or is there something I am missing?