Why is agreeing to a license required when signing up for an account with share.getwinc.com?

This Winc community site is intended to provide and maintain a common location where all Winc users worldwide can create, freely share, and develop upon each others learning resources. To that end, we require that you and every other Winc archive creator who wishes to share on this site agree to be bound by a common license. This ensures that all parties are on even footing, and that the Winc community can equally share in all resources. All the archives found on this site are meant to be accessible to anyone without restriction and any creator can use that content, share it with others, or create a derivative work that is customized and personalized as per their needs. Without determining ahead of time what license to use, its assumed that the archives you upload are copyrighted by you regardless of it you intended to share it, or wanted it to be public domain.