Politeness trumps communication first of all... also people can mean something at one time, and not mean it the next day. Their feelings on it changed, or they did not think it through.
Back when I was a social thing and DJing, doing music, etc... I might run into someone and talk to them and hit it off, and they might say something like "Yeah we should hook up sometime and jam do some music." And I will say and mean "Yeah sounds like a good idea!" Then realize that the person I was talking to lives an hour and a half away... and my work schedule is changing... or just upon retrospect I really don't want to.
So... I try not to say to the person: "I liked you that night, but you are not important enough to me to make me go out of my way or change my priorities." Because saying something like. "I got really busy sorry." Is nicer but not as sincere.
Even now... the DGN gatherings at red apple... I live about 15 minutes away, closer than a lot of other DGN people... but I can not see, with kids, work, pets, general lack of free time how I can go to one of these events, no matter when or where they are. It sounds crappy, and to be honest it is.... but it's the truth.