I think I get bored because I'm a family aspect type player and Generations and Aspirations were my two favorite expansions in Sims 3 so I go through these bouts of boredom where I step away. But I always come back and binge play for a long while lol.
That and I have large family sims and with University and how it plays, it messes with my ADD real bad and overwhelms me easily, lol. So I have to take breaks. I wish the semesters worked a bit differently so I didn't feel like once I enrolled a sim in college I was "stuck" playing them to the end of it.