Because it is still an issue and still nothing done about it : It is an enhancement request since it is not even possible to put a symmetry line for simple situations!
See added image.
I tried to place a sym line (Aux geo => sym line) on different
symmectrical entities but nooooooo he will not draw that sym line.
I dont know if it is a bug. But i do know i want this to be possible. And not by using a workaround. Just by doing what it has to do.