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.