Why? I think there are several reasons. One is that being mean makes you stupid. That’s why I hate fights. You never do your best work in a fight, because fights are not sufficiently general. Winning is always a function of the situation and the people involved. You don’t win fights by thinking of big ideas but by thinking of tricks that work in one particular case. And yet fighting is just as much work as thinking about real problems. Which is particularly painful to someone who cares how their brain is used: your brain goes fast but you get nowhere, like a car spinning its wheels.
Startups don’t win by attacking. They win by transcending. There are exceptions of course, but usually the way to win is to race ahead, not to stop and fight.