Maybe, if they would leave a message when the answering machine gives an opportunity, instead of hanging up, they might get a positive response via a call-back if we are interested in what they're selling.
Unfortunately, by intruding with the phone call, they choose to be a nuisance, as opposed to accomplishing their supposed goal of selling goods & services.
We would prefer no solicitation calls, however, they might as well divulge why they're calling, if they're going to waste time & effort with a phone call.