It must be logging the details only when there is a failure. Try copy some folder which doesn't exists, mention a fake folder name in Copy activity.
Reference - https://learn.microsoft.com/en-us/azure/data-factory/copy-activity-data-consistency
Above doc says -
The session log contains inconsistent files only, where the successfully copied files are not logged so far.
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Please don't forget to Accept Answer and Up-vote if the response helped -- Vaibhav