Whitepapers are to lure investors. Don't get me wrong, but many whitepapers are just full of bullshit and have very little value/ juice = technical descriptions, detailed info on devs plans.
This trend started few years ago, when people started saying that no whitepaper = scam.
Today I would say it may be exactly opposite.
Recently I was looking on Steem (Steemit.com) history and they started with no wallpaper of all, hell, they haven't even post description of their project.
It's just another trick for a lot of these scammers. Some ICO's take them very seriously and put a lot of time and effort into them, don't get me wrong. But those that just make things up to give it a nice shiny look are usually just looking for a pump and dump, if even that much.
Anyone can draw up a nice looking forecast and roadmap using some numbers and concepts that they like. The real question is if they can abide by that schedule and follow those promises. Because in the end, a white paper is nothing more than a piece of paper, if that.