Why don't I feel bad?
How come you don't feel bad?
I don't know.  How do you think I should feel about this?
If you have done something wrong, then you should feel bad because you recognize that it has hurt others.  Otherwise, it is still bad to appear too apathetic toward others, as they will think that you don't care about them.
I have no idea since the world is a huge cesspool. It's not like the feeling of guilt went away. I'm apathetic towards most things.
The world can be a depressing place sometimes if you let it. Try to see the positive and silver lining in life and you may start to cheer up.