Because Steemit is a corporation. They're incorporated, it's the way of the road, the way she goes! It's a business.
It's just a logo. They made the logo and it's them being like "this is MINE, this is US, this is OUR logo, this is OUR property!" Standard copyright stuff. No big deal at all.
It's just a big fat S. Nothing to get worked up over.
It looks very hungry though. What does it eat?