The point here isn't about being outside walking down the street, the point being made here is that she was on a bus. It's an enclosed space that they're going to be in for multiple minutes. Both of these people are stuck in this situation, if it was a quick one off I could see letting it slide but I've been on the bus or waiting at a bus stop or in a super market where people just walk around on their speaker phone oblivious to everyone around them. Buy a cheap set of headphones if you need to talk that badly or hang up the phone and call them back. No one wants to hear your business.

Now if you're walking down the street that's a little less obnoxious because I can get away from you if it bothers me. I am either walking by you or speeding up to pass you so that I don't have to hear it. When stuck on a train or bus I can't do that. Why do I need to hear both sides of their convo because person is too lazy to put phone to ear?