Because, believe it or not, we're not all considered as important as the president of United States or the head figure of one of the most popular religions. Therefore, we're not all treated that way.
You might think that your time is as valuable as theirs -- and I'm not arguing either for or against it -- but the fact is that you would be a minority and the world doesn't work the way we think it should, but the way majority decides (or is led to decide). And the world's that way not just when it comes to phone calls.