Multitasking exists in the sims 3 as well, but it's treated differently by the game.
In the sims 4, the game just switches these tasks at regular intervals, so the sim stops task 1 to do task 2, which takes time because the game treats them as two different actions. As an example, let's say you want your sim to eat (which I'll call 'task 1') and talk to another sim (task 2) simultaneously.
In this game, sims don't really multitask, the ai just 'switches' through multiple actions. Multitasking itself isn't the problem, it's the way it's implemented into the sims 4.
