Why do hipsters wear vintage?

It's obvious to see that most hipsters look like fashion history threw up all over them.  Yes, hipster, I see your clever mish-mash of 70s high waisted jeans, your awesome 80s wayfarers and ironic 90s "M.A.S.H." tee, what I don't understand is why is do they purchase these items instead of just going through you mom's closet.

I suppose today's fashions are too functional and that always gets in the way of coolness.