Using few words helps you say what you really mean. Using few words helps you focus your message. Using few words reduces the fluff and the repetitiveness. Using few words makes you work. There’s a comfort to the idea of the next paragraph. You think to yourself that if someone doesn’t quite get what you’re saying here, then he or she will for sure get it when the next group of words are read. Perhaps. But if this stuff is boring the next paragraph won’t get read anyway. And the work that would go into those extra words would go to waste. Best to spend the time that would’ve been spent on all those other words on these few instead.