Something That Amazes Me About Mail

I like our post office system but it amazes me that I receive so much junk mail. Everyone that I know throws their junk mail in the trashcan. So if everybody throws their junk mail away in a trashcan without reading it why do companies keep sending junk mail. If they didn't stamps would cost a lot more but still who is responding to junk mail and why. I guess the same people that responded to those emails that try to get you to smuggle money out of another country.