Can a person just be anemic or is there a reason why they are anemic?

There is : An underlying cause and it can almost always be sorted out.

Depends...: It depends on how one defines the anemia. If your hemoglobin is just slightly below what is the low range of normal, you have no symptoms, and it has been that low your whole life, then there may not be a particular reason for it, nor do you need to treat it. That being said, most diagnosed anemia has a reason(s). Either your body is having problems making red blood cells, or you are losing them.