I answer phones at my new job (yawn). Why are people so rude on the phone?

I used to be an HR Professional and had a lot of high level duties. Now I'm a receptionist at a law firm. I now understand why some receptionists are so cranky. People are buttholes on the phone. What happened to respect and being polite? Even before I answered phones I was ALWAYS pleasant on the phone any time I called any place. I think it's common courtesy. My law firm doesn't represent criminals or divorcees so it's not like I'm getting really cranky people going through those things. Sigh..