Cell phone etiquette

Why is it that some people think everyone wants to know their business. Case in point, while on my way to campus some disheveled man gets on the bur speaking loudly on the phone. Apparently his Church demanded he either admits he is an alcoholic, or leaves the Church. He then went on about family drama. He spoke in a very loud voice the entire time, so no one even had a choice of whether or not to listen. You could see the other bus patrons getting visibly upset, but no one actually said anything ( including me). I guess because this guy looked and sounded a little bit off, like he had dome some time in a mental health facility. Either way I have never understood why people do such a thing, or want the world to know their business, especially when it's negative or unflattering to say the least!