Currently Staff Assignment will only allow you to set a max column to 8. There are plenty of use case scenarios where temporary roles require more than 8 users to be assigned at once. Many end users prefer to add themselves to any/all temporary roles/groups in staff assignment rather than by voice, as it saves time. It's scenarios like this when a group has potentially more than 8 members at once where it would be beneficial to allow multiple members, or redesign the interface to allow the user to add as many as they want (rather than having the fields being hardcoded).