The Sims 4 keeps pushing the whole emotions system as a major feature, which it is, but it also says on it's packaging that Sims experience emotions "for the first time" which isn't strictly true. The Sims in Sims 3 had emotions, they were just tied to the mood bar, which meant not a lot of them were seen most of the time - but they were still there. Furthermore, traits actually impacted what emotions your Sim would feel. It's absolutely by no means a perfect system at all, but it should have been the starting point for the system used in The Sims 4.
https://i.postimg.cc/fywTH84F/Emotions.png