How many people have you ever walked up to and just started chatting about their pasts, and political views? Zero, that's what i though.
Sometimes people just dont want to talk to some random person. We live nearly all our lives not talking to 99.999% of the people we come across in our lives. So its not unrealistic at all, or less "alive" when a game does the same thing. Why would they want to talk to you anyway? All it is is you asking questions and only giving small one liners back. A very boring conversation if I do say so.
That's why I said "every character you could talk to" and not "every character in the gameworld". As in Skyrim, there are many characters who you can't talk to and who only spurt one-liners. Most characters with whom you can talk, have a reason for talking to you: a shopkeeper, a quest giver etc. And believe it or not, asking a shopkeeper "How are you?" or "So, what's your story?" isn't unheard of. I do it IRL on occasion.
In my opinion defending NOT being able to talk to people in an RPG is pretty much screaming "LALALALALA I can't hear you, this game is perfect because it's TES, I don't care how many features are left out or are done better in other games. I would love TES no matter what because I am a really devoted fan!" (Which isn't a bad thing, we all have something we defend irrationally despite it's flaws. Like don't try to criticize Vampire the Masquerade: Bloodlines in front of me, or I'll explode ;P ) But that's off topic.