Why aren't you allowed to say "I have been knowing her for ten years" or "It has been broadcasting for many years"?
But you are allowed to say "I have been waiting for an hour".
Learn English – Present perfect continuous and “for”
grammaticalityprepositionspresent-perfectprogressive-aspect
Best Answer
Knowing happens but once -- unlike waiting, you don't stretch the process of knowing someone over an extended period. It happens at a moment of time. That is why, I suppose.
You could, on the other hand, be getting to know the person better over ten years.