Is common courtesy dead?

I think common courtesy is dead, or, at least, very ill and possibly terminal.

I don't understand why it's so difficult for some people to respond to emails just to them asking direct questions (but respond to the silly emails about the latest updates about Angry Birds).

I don't understand why it's so difficult for some people to make plans with people they supposedly care about, or even respond to invitations at all.

I don't understand why it's so difficult for some people to not leave other people hanging.

I don't understand why instead of answering the question "Where is the stuff I left with you when I moved away from The Homeland?", some people will not only not respond, but actually defriend you from Facebook.

I don't understand why it's so difficult for some people to say "I'm sorry" when they have to bail on plans you've made together.

Now, I'm not perfect, but I at least try and do these things. It's just polite.