You are performing the migration of Opportunities and observed that the Distribution Channel field is not mandatory in the migration template. But in the migration template for Employees, the Distribution Channel field is mandatory. You would like to know, why there are different approaches.
Due to this fact it could be that migrated Opportunities are not visible for the Employee, because there is a Distribution Channel maintained in the Employee master, but not in the Opportunity.
This is expected system behavior.
The fields which are mandatory in master data like employee will not be mandatory in transaction documents like opportunity. These are completely different use cases. From opportunities perspective this is not a mandatory attribute.
If you want to keep such a check then you can add a PDI validation to prevent save of an opportunity where distribution channel is not maintained. Then in all cases, including migration, you will always have data where this is maintained.
KBA , LOD-CRM-EMP , Employee , How To