A third reason may be that you know there is something better out there, but this is what you studied for, so it must be it, right?
I have had this discussion with friends in my marketing and communications circles and some share comments that make me think: "You definitely should not be there" and some where I think "You definitely should stick around". What differentiates the two?
You definitely should stick around:
If you are good at exercising your opinion and ideas - guess what? This is tailored specifically for young'uns in the marketing and communications industry. This industry is about the product or the people. And these two things are things that change.
You need to be comfortable with change because it keeps you on your toes and without it, you are not growing. It is not easy to deal with change all the time, but if you are the "stick around type" you will make it through.