The Sims 4 was originally intended as a low-budget, online multiplayer game. The problem was not the online mode, but the development conditions, which happened in a very bad period at EA, with absurd predatory practices. Not that today is much different, but back then, all games had to have online features.
They just decided to remove the online mode after the SimCity failure. And they removed online when there was little time left before the game was released, just over a year and a half. This meant that many things had to be redone on top of the wave, which explains why the base game was released with so many missing features.
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About The Sims 5 multiplayer, there are no secrets. The game is not an MMO like Second Life. We won't find players from all over the world like in The Sims Online from 2002.
You can invite some friends from your EA App / Origin to play the game with you, in a kind of private room, where you and your friends can play together, and customize the game together. The whole game will be made taking into account the gameplay with friends, but it will also work for those who want to play alone.
That's why Grant made it clear: The Sims 5 can be both an offline and an online game. When you want to play online with your friends, you can. When you want to play offline alone, you can.
