Writers get tired of waiting for responses, getting unexplained rejections, receiving notice that a manuscript was lost, or finding out that the story is no longer appropriate for the publication's format. So they pick up an issue of Outer Darkness , Epitaph or Flesh and Blood and think it's something they want to do. While you're reading something someone else wrote, you're not writing. Most zines pay only in contributors' copies, which should tell the potential publisher that, at least in the first couple of years, no profit's involved. Some publishers don't consider this and assume money is being made, or so many people wouldn't be publishing.
New publishers advertise their guidelines and expect the money to start pouring in.
Those that make it to the first issue usually publish two or three issues before folding. Many small press publications fold without returning subscription money, leaving a bad taste in the mouths of those who would subscribe to new publications. Setting aside financial and time issues, there is an up side to producing a publication. As a small press editor, I get to read work from writers who have never sent out a poem before in their lives. Now granted, some have no business submitting in the first place, but when something crosses your desk that sends off fireworks in your head . . .