Because we’re the most evolved species and have found ways to control both our own actions and that of other animals. We’ve developed language, politics, economics and religions- it is a bit more than the animals have achieved so far!
We rule the earth because we can. We’re smart enough to have pretty much unlimited manpower at our disposal, which means we can solve any problem really quickly if it’s profitable to do so. If we were stupid at an individual level, it’s possible we would have died out millions of years ago, and a giant slug might rule the earth!