Sooo Why cant unplayed sims make their own decisions (Marry,Children and Dating)

Yeah what im doing now is repopulating, Lots of woohooing and adopting here and there... SO how would i go about playing with genetics if the household is already in the map... Thank you for all the comments. This really bothers me that they dont even have the option. Im spending a lot of time repopulating and not enough time actually building and working on the families i wanna work on