Perhaps because we are so good at making everything the way we want it to be?
Maybe it's because we can live anywhere. By destroying everything else that can survive in that habitat.
OH, I know, because we have so many varieties of us all over the world.
Or it could simply be that very taboo word:
We are so good at thinking we are the best at anything we set out to do, no species could ever compete. We MUST be the most adaptive. Because we must.
That quirky humanity.