The reason for calling is because it is harder to deny someone that you talked... Duh, human psychology. When you interact with human beings, it create a connection and rapport. It's hard to break that bond, after a couple of jokes. If a human likes you, he is more willing to assist you in what you need and your endeavors... This is how humanity works... is it logical... no.
Have you ever noticed that the idiot managers/boss are always the guys that have great stories or are fun to be around, but don't know shit about their job. Why do you think that is? It's because they create a rapport. Am I drunk on a thursday afternoon, yes... because I created rapport with my bartenders...