So do I, but plenty people want MP.

However adding MP to a game is never as simple as those people claim it is. Now your game has to handle the connection, data sharing, making sure all MP players are seeing the exact same thing. And it needs to do it with good performance, because laggy MP is hell. It’ll probably need a server too, either external or one of the players - the later having performance costs. Balance is often thrown out of the window and needs adjustments, because as soon as you add another player into the game they gather resources 2x faster together.