Why are topics associated with contacts instead of mailing lists?
Each contact may have multiple preferences. This means associating a contact with relevant topics is an easier and more efficient way of organizing and storing the contact preferences.
If multiple topics are not required for your organization as you solely focus on sending generic email marketing campaigns or for any other reasons. You can simply use the default topic. This will be configured in your account if you've created a Zoho Campaigns account recently or if you've migrated to the new Topics flow.