Because growth is exponential and your resource income is too, there is always going to be a point where you get so much resource income, you don't know what to do with it anymore. Then if someone is new and you can help them, it won't really affect your own growth.

For them, a shipment of say 20k res, is an enormous amount they can build with for days, for you it is nothing. Other games don't usually have mechanics like this, or at least, carried to this extreme.

Then the fact that attacking people often gets you little reward makes it so that people aren't really interested in attacking. The few people that do attack weaker players, quickly get smacked down for being "nasty people" even though this would be considered normal in other games. In fact, if attacking would be more profitable, more would do it and the community reaction would be different. If everyone gobbles up their neighbour because it makes them stronger, noone will bother doing something about it. 

Of course the mechanics also draws a certain type of player so that this effect is magnified. People are nice because of the game mechanics and the game mechanics draw nice people to the game.