While I generally don't mind it being either way, I think it has to do with the previous sims games.
Sims has always been an escape from reality for many people and their place to do their things and control an entire world just for them.
I think people are also confused about the mechanics as time will be passing by when you are offline and you will not be able to move time faster, etc.
I think the sims franchise should stay singleplayer, perhaps add a new sims game (like sims mobile) for multiplayer. That would be cool.
