Answers are two:
- high cost (FreeCAD is not but surfacing in Freecad is opposite of MoI),
- pure procedural workflow is less creative I think. It`s easier to change something but harder to make many creative iterations of design because design process is slower. Parametric surfacing is also not so fast and not so good (maybe I`m wrong).

I think design in MoI is very fast and that is biggest advantage of MoI in my opinion.