Why do they do this?
I personally try to take as many neutral (undefended) outposts first.
The way I see it: The less factories you have, the greater the sacrifice when you attack someone (or when you defend against an attack) and lose drillers in this battle because it will take much longer to produce that many drillers again.
So why would I attack someone right at the beginning of the game? This will only lead to both players (attacker and the one being attacked) having less drillers and therefore being at a disadvantage for the first few days. Time and drillers spent in battle are kind of wasted because they could have been used to take neutral outposts first.