If you cannot get hurt by people you dont really care about them anymore. If you dont care about them, they cant be your friend. You wont let them get close enough to actuallly matter to you.

As for people not caring anymore, well you yourself state that you dont care anymore. They have probably developed the same attitude, its a difficult world too live in. Everything goes fast and if you cant keep up your screwed. Lots of people arent cutting it these days and harden themselves to stop hurting.