Explanation: MailChimp enables users to create custom sign-up forms with custom required fields. Rafflecopter can only support required fields that it recognizes. These include email ("EMAIL"), first name ("FNAME") and last name ("LNAME").
Because Rafflecopter already has this information for each entrant, the entrant is not required to enter any additional information which leads to better conversion. If one of your lists is missing from the dropdown and you'd like it to appear, please uncheck "Required Field" on any custom fields in the MailChimp form creator.