This is an age-old question. Seriously: there's [an MSE thread](http://meta.stackexchange.com/q/1576/165581) about this that's five years old. 

My two personal favorite explanations: 

> I see it more as a consolation prize. No one looked at your question or answered it, so here's something to hold you over until you get an answer.

-- http://meta.stackexchange.com/a/1579/165581

> ...it's the the engines way of saying "Sorry, I couldn't get you an answer. Please forgive me :("

-- http://meta.stackexchange.com/a/1653/165581