Perhaps it is because as the series progresses, small-scale iterations become less and less impressive, with The Sims 2 scoring higher than the Sims 3 and lower than the Sims 3. 

The Sims 2 is an exercise that adds depth, giving the Sims a clearer personality type, and even influencing them with constellations and ambitions. 

The game also provides direct control over the Sims, which was not available in the original game. 

There is no "story" in the game, but some pre-built communities feature character arcs and short storylines.