And the person on the other end of the line often doesn't realize how uncivil the situation is. They might know they're on speakerphone, but they actually can't see that they're interrupting the trains of thought of dozens of people around them. This means the content of the conversation is more likely to be inappropriate for public consumption, making it even more distracting for the forced participants.

The person holding the speakerphone is to blame, of course, but they often seem to go into a state of pathological flow where they're almost as oblivious as their conversation partner.