Many of us fat ppl are also good at denial. I didnt say "I am fat" until I started to lose weight. But I was overweight for almost 2 decades. Various degrees of fat and overweight. I knew I was heavy and weighed too much. But never thought or said, I am fat. You think oh geesh, at least I am not Xlbs. And then pretty soon you are. And then you think, well at least I am not Xlbs! And then one day you are. Once the initial shock wears off, you just settle in to what it is. For the most part, I never used a scale so it was easy to be in denial. DH still loved me, we enjoyed most every evening out together --- eating out. I never (hardly ever) cooked at home.
I do think plenty of ppl do say they are fat, but I know for me, it took me a long time to get to that place of saying it outloud. I really don't think I said, "I am fat" until I had already started to do something about it, which may be why you hear it frequently if they are already at a place of working on it. Even now, I still think I am okay or at least maybe not so bad, until I am reminded by a picture that I am still a long ways from my goal. I spent so many years hiding from the camera, and if I didn't see it, it must not be true.