Omg, this has been my biggest complaint for a few years now. It's so weird, isn't it? How did Fear get left out of a Sims game that focuses mainly on emotions?
I've been requesting a lot for the devs to put the time in to add Fear, but they did say once that it would be a huge undertaking to add it. Not impossible, mind you, but a lot of time and work. In the end though, I really think it would be worth it. Things just aren't right without proper fear. I'm also hoping that they expand on it and do an entire phobia system so we can choose specific things that our Sims are afraid of, like spiders, bees, thunder, vampires/ghosts/aliens, failure, children turning out bad, etc. I think if something like that were put into place, it would really fill in the gap and make the Sims more realistic and engaging as well.