Why are fields missing from the data wizard mapping screen?

The data wizard has its own field mapping, separate from the Mappings setitings, so that you can customise your imports as needed. To have access to a field from Salesforce in the data wizard mapping, you will need to include it in the source you specify on the first steps of the wizard. 

• List views and reports: Add the fields you want to map as columns in the source. 
• SOQL: Add the fields to your SELECT statement.
• Campaigns: The fields must exist on the Campaign Member object. To access contact fields, you will need to add formulas to that object. Consider using a report on Campaigns and Campaign Members instead, to save time building formulas.

Note- If you change any fields on an existing import source, be sure to walk through the wizard again to update its mapping. You can do this from the data wizard list by clicking the wizard name. We recommend storing list views and reports used in data wizards in a special folder with restricted sharing, to avoid someone accidentally updating the report unrelated to the wizard, as well.