I'd like that this topic was clear, and of course there are surely different types of motivations but a major one is the value given to that time and the meaning that you cannot pretend not to understand to the game itself.
If I join a space sim, we want to meet other players. At the same level of importance there is fair competition for the assets, it's a strategic game,it is many things, so I want to find other players, no matter what I do that do face same challenges as me. I want to enjoy their behavior, no matter what this is. And we are all sure that these behaviors will create content, create consequences, they will be cause of gameplay.
Yes, the game is a sandbox, this is actually its major weakness, in the sense that it is surely a plus (if u manipulate my words or take the meaning of sandbox I don't mean here) for the aspect of "do what you want in such Space\galaxy", but it's WOULD BE a major driver of players if all were abiding to a set of rules like playing open, incentive to play open, etc etc.
What game is there if you come to the table in other terms from a common agreed ones? This is not a topic that tries to discuss wether there is chance for single player to meet multiplayer. It's just offensive to think that multiplayer people need to do additional effort to do stuff that you can do offline by cutting short the game (and because you find it fun) it does force other players to or abandon or to actually deploy extreme measure to counter that, into something that is innatural and also against fun and sustainable gameplay.
The "wanna be everything" it is confirmed by piles of knowledge of ART design is the reason why projects do not work, design must decide a direction cannot be fish and meat at the same time as this game does. This is a major weakness of this game, not a strenght 100%.
