Sims 4 Sims are in general a lot more social than Sims 3 Sims - to a point that really gets on my nerves, because nothing gets done. I´m always like, stop chatting, do the thing that I told you, gosh dang it!
I did a asylum challenge (you play with 8 insane/erratic sims, only controling one) once, in Sims 3 and Sims 4, trying to make them as similar as possible (traits and looks). The Sims 3 Sims usually ran off doing things based on their traits, interacting only when their social was low. The Sims 4 Sims always hung together chatting all the time, doing little else.
If you want your Sims 3 Sims to interact more, it helps, if there is not much to do for them - meaning, no pc, no television or other fun stuff. They will do a lot more with each other.