Well it is successful but not as overly-successful considering the circumstances of
1. how often the game has been free or very very cheap and people might own it and not play.
2. Bundles it was given away with people bought and got the Sims 4 with it for free and have it now abandonded in their libraries.
3. In order to play the Sims 4 on your Steam account you have to rebuy the base game (so a lot of people own the game twice).
No doubt it's a successful game but it's important to see what may have contributed to these numbers. Also numbers don't equal quality or enjoyment but that's another story.
